This way we can depend on alpine's python3 package which is binary
compatible with the rest of the python packages in the distribution.
This requires spelling out python3 explicitly in several places since
alpine still defaults to python 2 for /usr/bin/python.
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.