Started port to Django 2.1, Python 3, Docker

This commit is a rough port to Django 2.1, Python 3 and a Docker based local
development setup. Tests fail/error but migrations and the web frontend are
already runnable. Task queue functionality is untested and translations seem to
have trouble.

gnuviechadmin/osusers/views.py

@@ -4,8 +4,8 @@ This module defines the views for gnuviechadmin operating system user handling.
 """
 from __future__ import unicode_literals, absolute_import
 
-from django.core.urlresolvers import reverse
 from django.shortcuts import redirect
+from django.urls import reverse
 from django.views.generic import (
     CreateView,
     DeleteView,