This commit updates the docker image to be based on Debian 10 Buster.
The startup script waits until the database container becomes available.
Needed dependencies for building the PostgreSQL driver were added to the
docker image.
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.
