Move from pylons to django framework

Pylons is unmaintained and a new framework is needed for mentors.

Django is the next logical choice since it's well maintained and most of debian python website use it.

Initial work has been done in this repo: https://salsa.debian.org/mentors.debian.net-team/mentors-django

There was also a bit of work on that commit: 0c84a39b (note, this was not merged to live since it contains only a small skeleton for a django project)