* Test dependabot for Dockerfiles.
* Also for github actions
* Update dependabot.yml
* Fix urls.py for new versions of Django
* Fix urls.py for postorius.
* Bump dependency on Postgresql.
* Bump dependency on Django
* Add dependency on tzdata.
This commit adds a lot of new code including the mailman's web
frontend. It includes a configuration file which can later be
configured to run required configs.
Also, the docker-compose file spins off the containers, sets up
appropriate volumes and links.