Rework event sequence

No more FRAMEBOUNDARY, no more PRERENDER in the sense it once meant.
PRERENDER is what was POSTUPDATE.
UPDATE is now PREPHYSICS.
PREUPDATE is now PREINPUT.

Stopgap object system now autosubscribes to PRERENDER instead of
PREPHYSICS because it makes earthball's code be cleaner.
Add a user data field to MNCL_OBJECT