Support latest stable version of Python and Django

[pauloxnet]

I propose to update the support and tests to the current stable versions of Python and Django removing unsupported versions (e.g. Python 3.5 and Django 3.0).

Right now the active Python releases are:

• 3.6
• 3.7
• 3.8
• 3.9
• 3.10

The current Django supported versions are:

• 2.2
• 3.1
• 3.2