Fix mobile detection with django-user_agents

This PR fixes the Scout app's mobile detection by removing django_mobileesp and replacing it with django-user_agents (django_mobileesp was actually an alternative to django-user_agents to begin with, but the later is still being updated and the former is not).

Just look at how stylish this new mobile view is:

And of course, migrating to Django 2.x stuff as I find it--this time, {% load staticfiles %} -> {% load static %}.

Please review: @NUWAN.KUMARASIRI @TREFILEK @bjsousa