Split python2 and python3 packages and update to newest versions:
  * python-django-restframework version 3.9.4 using django1
  * python3-django-restframework version 3.11.0 using django3
This fixes the issue that the restframework cannot import name
'python_2_unicode_compatible' from 'django.utils.encoding', when
using version 3.9.x together with Django 3.y.

Signed-off-by: Peter Stadler <peter.stadler@student.uibk.ac.at>