[z2230] EventAI: Add new TargetTypes

Add target types:
* TARGET_T_ACTION_INVOKER_OWNER which returns the controlling unit of an action's invoker
* TARGET_T_HOSTILE_RANDOM_PLAYER which returns a random player from the threatlist
* TARGET_T_HOSTILE_RANDOM_NOT_TOP_PLAYER which returns a random player from the threatlist except topmost threat holder

Also remove unused CreatureEventAI::CanCast function

(based on commit [12329] - 7b674f2)

(based on commit [s1867] - df03828)