MCPServer: replace databaseInterface with Django models

`databaseInterface` is still imported in a few places in MCPServer, primarily for the `getUTCTime` function that will be moved elsewhere, and for database locking that may be removeable.
Since it's semantically a boolean, I think it makes sense to have the field reflect that.  I think BooleanField is more correct for this case, but since the DB allows NULL, then NullBooleanField may be better?  OTOH, if we want to eventually generate the tables from the models, BooleanField is what we're really want.