Not having prefer-const on the JS side makes JS -> TS refactors really
unreadable. This commit just auto-fixes it so we're using
`prefer-const` everywhere.
- The big change here is that player.userid can now be empty. You can
now fit state into RoomGamePlayer subclasses even when there are no
users associated with them.
- `game.players` has been introduced as the new canonical list of
players, including userless players. The old `game.players` has been
renamed `game.playerTable`, for clarity.
- `game.addPlayer` now returns the added player
All existing RoomGames have been updated for the new API, and
RoomBattle is now officially a RoomGame subclass.
Tournaments was also massively refactored to be properly updated for
the old API, since that never happened, and should now be a lot more
readable.
