WIP replace hp/breath by generic stat mechanism

This is not compatible to current servers and requires a min protocol bump.

Main benefits:
 -playerside stats (saved along with player not separate)
 -new lua hud statbar type bound to player stat
 -slightly reduced network overhead (now equals same as old c++ statbars)
 
Midterm benefits:
 -adding of new stats isn't core issue any longer
 -clients may read information about other items too

Longterm benefits:
 -stat values could be evaluated by client side lua code too

Open issues:
 -compatibility
 -strange behaviour on death (almost always within own bones)
 -add support for lua entity stats too