Minimum changes to make it work for Djnago 3.2

[uzi0espil]

These are the changes:

• Fix imports and deprecated methods coming from Django.
• Override and remove the navbar that has been introduced in Django 3.1
• Fix styling issues:
  • Right filter in changelist not showing.
  • missing jquery library.

I haven't updated the demo site at all. So there might be something to be fixed there.