Backport AI and combat improvements from wotlk branch

Bots have better management of:
- healing
- DPS
- Buffing
Bots can now:
- Dispell (mage and magic for priest are WIP)
- drink/eat (not 100% working yet)
- pull mobs (not 100% working yet)
- Use elemental resist orders
- wait before engaging ennemies, letting some time to the tank for building up its aggro
- save/restore their combat order (you must update your character DB for this)