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.
This commit add model classes closely matching the tables defined in
PowerDNS' schema as described at
https://doc.powerdns.com/md/authoritative/backend-generic-mypgsql/.
The commit includes the model definitions a schema migration including
PostgreSQL specific CHECK constraints and the registration in the Django
admin interface.
addresses #17
