Improve websocket join performance

[megamattron]

We're still averaging 1sec+ when joining, probably something slow in there.

[megamattron]

Notes to self, things still to fix:

• [x] ChatRoom.userCanPost - remove join find and getBannedUsersCall
• [ ] addConnection - check if we can call redis with no-wait for response
• [x] Don't call isModerator in addConnection
• [x] Preload last message caches on application start

[megamattron]

• [x] Check if user -> room join exists and skip all the join checks

[megamattron]

Performance seems solid now after the changes mentioned above:

20:59:06,892 INFO  ~ Websocket join time for megamatt2000: 89ms

Initial state loading is slower, but still pretty reasonable considering how much data I'm loading (I'm in most rooms):

20:59:00,086 INFO  ~ measure#fullstate.timing.load=430ms

Calling this closed for now.