text: Title: Stateless app loading hook exceptions should be captured and not propagated
  Body: A side effect of the misconfiguration in #330 is that it exposes a lack of exception handling around the hook to locate a stateless app.
  
  The code in [get_local_stateless_by_name](https://github.com/GibbsConsulting/django-plotly-dash/blob/master/django_plotly_dash/dash_wrapper.py) should cleanly capture any exception raised by the hook.
  