title: NoReverseMatch - 'viewflow' is not a registered namespace
body: <p>When trying to run the custom UI app ("parcel") for viewflow from the official <a href="https://github.com/viewflow/cookbook/tree/master/custom_ui/demo" rel="nofollow noreferrer">cookbook</a> I get this error:</p>
  
  <blockquote>
    <p><strong>NoReverseMatch</strong> at /parcel/delivery/5/start/21/detail/ 'viewflow' is not a registered namespace</p>
  </blockquote>
  
  <p>I took a screenshot: 
  <img src="https://i.stack.imgur.com/FC3Km.png" alt="click for image"></p>
  
  <p>Here's the traceback:</p>
  
  <pre><code>Environment:
  
  
  Request Method: GET
  Request URL: http://localhost:8000/parcel/delivery/5/start/21/detail/
  
  Django Version: 1.10.7
  Python Version: 3.4.0
  Installed Applications:
  ['django.contrib.admin',
   'django.contrib.auth',
   'django.contrib.contenttypes',
   'django.contrib.sessions',
   'django.contrib.messages',
   'django.contrib.staticfiles',
   'material',
   'material.frontend',
   'viewflow',
   'viewflow.frontend',
   'apps.parcel']
  Installed Middleware:
  ['django.middleware.security.SecurityMiddleware',
   'django.contrib.sessions.middleware.SessionMiddleware',
   'django.middleware.common.CommonMiddleware',
   'django.middleware.csrf.CsrfViewMiddleware',
   'django.contrib.auth.middleware.AuthenticationMiddleware',
   'django.contrib.messages.middleware.MessageMiddleware',
   'django.middleware.clickjacking.XFrameOptionsMiddleware']
  
  
  Template error:
  In template /Users/paul/delete-viewflows/templates/parcel/delivery/task_detail.html, error at line 0
     'viewflow' is not a registered namespace   1 : {% extends 'viewflow/flow/base_task.html' %}
     2 : {% load viewflow %}
     3 : 
     4 : {% block nav_parcels_cls %}class="active"{% endblock %}
     5 : 
     6 : {% block task_actions %}
     7 : {% flowurl activation.task 'execute' user=request.user as execute_url %}
     8 : {% if execute_url %}
     9 : &lt;a href="{{ execute_url }}" class="btn primary"&gt;Execute&lt;/a&gt;
     10 : {% endif %}
  
  
  Traceback:
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/urls/base.py" in reverse
    77.                 extra, resolver = resolver.namespace_dict[ns]
  
  During handling of the above exception ('viewflow'), another exception occurred:
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/core/handlers/exception.py" in inner
    42.             response = get_response(request)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/core/handlers/base.py" in _get_response
    217.                 response = self.process_exception_by_middleware(e, request)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/core/handlers/base.py" in _get_response
    215.                 response = response.render()
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/response.py" in render
    109.             self.content = self.rendered_content
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/response.py" in rendered_content
    86.         content = template.render(context, self._request)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/backends/django.py" in render
    66.             return self.template.render(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/base.py" in render
    208.                     return self._render(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/base.py" in _render
    199.         return self.nodelist.render(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/base.py" in render
    994.                 bit = node.render_annotated(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/base.py" in render_annotated
    961.             return self.render(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/loader_tags.py" in render
    174.         return compiled_parent._render(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/base.py" in _render
    199.         return self.nodelist.render(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/base.py" in render
    994.                 bit = node.render_annotated(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/base.py" in render_annotated
    961.             return self.render(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/loader_tags.py" in render
    174.         return compiled_parent._render(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/base.py" in _render
    199.         return self.nodelist.render(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/base.py" in render
    994.                 bit = node.render_annotated(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/base.py" in render_annotated
    961.             return self.render(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/loader_tags.py" in render
    174.         return compiled_parent._render(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/base.py" in _render
    199.         return self.nodelist.render(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/base.py" in render
    994.                 bit = node.render_annotated(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/base.py" in render_annotated
    961.             return self.render(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/loader_tags.py" in render
    174.         return compiled_parent._render(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/base.py" in _render
    199.         return self.nodelist.render(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/base.py" in render
    994.                 bit = node.render_annotated(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/base.py" in render_annotated
    961.             return self.render(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/loader_tags.py" in render
    174.         return compiled_parent._render(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/base.py" in _render
    199.         return self.nodelist.render(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/base.py" in render
    994.                 bit = node.render_annotated(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/base.py" in render_annotated
    961.             return self.render(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/loader_tags.py" in render
    70.                 result = block.nodelist.render(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/base.py" in render
    994.                 bit = node.render_annotated(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/base.py" in render_annotated
    961.             return self.render(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/loader_tags.py" in render
    70.                 result = block.nodelist.render(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/base.py" in render
    994.                 bit = node.render_annotated(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/base.py" in render_annotated
    961.             return self.render(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/loader_tags.py" in render
    70.                 result = block.nodelist.render(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/base.py" in render
    994.                 bit = node.render_annotated(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/base.py" in render_annotated
    961.             return self.render(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/defaulttags.py" in render
    209.                     nodelist.append(node.render_annotated(context))
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/base.py" in render_annotated
    961.             return self.render(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/defaulttags.py" in render
    315.                 return nodelist.render(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/base.py" in render
    994.                 bit = node.render_annotated(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/base.py" in render_annotated
    961.             return self.render(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/base.py" in render
    1044.             output = self.filter_expression.resolve(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/base.py" in resolve
    711.                 obj = self.var.resolve(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/base.py" in resolve
    852.             value = self._resolve_lookup(context)
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/template/base.py" in _resolve_lookup
    915.                             current = current()
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/viewflow/frontend/apps.py" in index_url
    55.         return reverse('viewflow:index')
  
  File "/Users/paul/.pyenv/versions/dj-viewflow/lib/python3.4/site-packages/django/urls/base.py" in reverse
    87.                     raise NoReverseMatch("%s is not a registered namespace" % key)
  
  Exception Type: NoReverseMatch at /parcel/delivery/5/start/21/detail/
  Exception Value: 'viewflow' is not a registered namespace
  </code></pre>
  
  <p>I tried to look for an <code>urls.py</code> in viewflow to include in my project urls but couldn't find anything. </p>
  
  <p>How can I fix this? </p>