* Use AI::AttackStart calls only in case explicit request creature attack from core or AI code "attack it if can".
Like taunt, pet handler attack command.
* Use AI::AttackedBy for reaction at hostile action "do something at hostile action"
Like non-dot damage, swing, negative spell landing, or fade fear/etc.
And provided by default call AttackStart if no current target.
This fix some problems, like:
* Civilian will react propertly at attack by another creature (not pet or player).
* Will not cases (at least triggred by core) when attack target start run to attacker before any real hostile action apply.
Also send pointer to AI constructors ans mark constructors as explicit.
This changes allow move now some generic often used AI code to CreatureAI helper functions.
