Move lobby members off redis, few logic fixes for possible lobby-join exploits

- Moved members to an arrayfield, helps with some querying logic, moves
weight off redis for things that don't really need to be in redis (e.g.
a list of 5 items)
- It was possible for a user to own muiltiple active lobbies, thats
patched (although the backend code is just todo'd out)
- It was possible for a user to be in multiple lobbies at the same time,
thats fixed by removing the user from other lobbies before joining a new
one.