title: RuntimeError: Model class doesn't declare an explicit app_label and isn't in an application in INSTALLED_APPS for Django OAuth Toolkit
body: <p>I want to access the models that are used by Django OAUTH Toolkit so I can periodically delete old tokens from the database. I thought I'd just import them:</p>
  
  <pre><code>from oauth2_provider.management.commands.cleartokens import Command
  from oauth2_provider.models import AccessToken
  Command.handle()
  </code></pre>
  
  <p>However when I try to run this file in the command line I receive the following error: </p>
  
  <pre><code>Traceback (most recent call last):
    File ".\db_cleanup.py", line 5, in &lt;module&gt;
      from oauth2_provider.models import AccessToken
    File "C:\Users\User\.virtualenvs\gsm-django\lib\site-packages\oauth2_provider\models.py", line 178, in &lt;module&gt;
      class Application(AbstractApplication):
    File "C:\Users\User\.virtualenvs\gsm-django\lib\site-packages\django\db\models\base.py", line 95, in __new__
      "INSTALLED_APPS." % (module, name)
  RuntimeError: Model class oauth2_provider.models.Application doesn't declare an explicit app_label and isn't in an application in INSTALLED_APPS.
  </code></pre>
  
  <p>I tried adding <code>oauth2_provider.models.Application</code> to my installed apps in my settings file as well but to no avail: </p>
  
  <pre><code>INSTALLED_APPS = [
      'django.contrib.admin',
      'django.contrib.auth',
      'django.contrib.contenttypes',
      'django.contrib.sessions',
      'django.contrib.messages',
      'django.contrib.staticfiles',
      'api',
      'oauth2_provider',
      'oauth2_provider.models.Application',
      'rest_framework',
      'rest_framework.authtoken',
      'graphene_django',
      'corsheaders',
  ]
  </code></pre>
  
  <p>I added <code>app_label</code> to the <code>Application</code> class it mentions as well, but that does not work either.</p>