Add support for getting clients in a given room (Works across multiple nodes)

I added basic support for the redis adapter for storing and getting clients (As an async call) or a room in the redis database.
I didn't manage to do the exit cleanup correctly, so after normal exit, rooms are still filled up with the same (now unexisting) socket ids. Quitting with Ctrl+C or the kill signal should work as expected.

Also added a test for the clients function call