Use Bunch class for multiplayer.

This requires that bunch stores chars instead of Tile pointers.
(WIP) Attempt to refactor menu system

Currently changing selection doesn't work
More menu refactoring

Now entries handle their own selection action in process_event, so the
menu only has to forward things along. Menu actions that change more
than internal state are now handled in main using pending checks. This
means we don't need any reference-storing entry classes like QuitEntry
and SinglePlayerEntry
Fix menu selection sounds/errs. Fix quit segfault