Add docstrings for the classes & globally

This should be a good habit to keep for me
Sync routes to Redis as they are added and deleted

Canonical source is always the db - so we do not do anything
in Redis until the data has been commited to the database
Add POST method handler to handle mapping updates

This way, domains can also be renamed easily. Redis updating
of renamed domans is also performed.
Add redis as a requirement in requirements.txt