This completely removes the previous DB patching mechanism.
When this is first run for an existing installation of Unwind, depending
on its version it might lead to problems because the database's schema
won't match the code.
To avoid that issue, when upgrading Unwind to this version make sure to
STOP the old application, install this new version but DON'T start it,
instead use `alembic upgrade head` to run the outstanding patches, and
only then start the application.
Among the many changes we switch to using SQLAlchemy's connection pool,
which means we are no longer required to guard against multiple threads
working on the database.
All db funcs now receive a connection to use as their first argument,
this allows the caller to control transaction & rollback behavior.
