Replace docker volumes with proper directory mounting

[tsunyoku]

The docker-compose setup was a little short sighted and used volumes for data over a directory mapping which has created an annoying problem of people not being able to as easily access the .data directory that bancho.py creates.

We should migrate to using proper directory mounting, but will need to make sure the necessary announcements & notices are made with instructions on how to migrate, as moving the data from the old volume to the new directory mapping will be required - this will not effect new users or manual setup users, only pre-existing users who opted for the docker method.

There is still some discussion which needs to be had on how exactly we want to achieve this, so please use this as the forum of discussion.

Treating this as a bug hence the p1, the current behaviour certainly isn't intended and even confuses bancho.py's own logic so...