[12474] AI-Event throwing and receiving implementation

Add new AI hooks to
* SendAIEvent (either around the npc, or to a specified npc)
* ReceiveAIEvent (hook to receive sent events)
[12475] Add ACTION_T_THROW_AI_EVENT and EVENT_T_RECEIVE_AI_EVENT to EventAI

Also introduce new target-type TARGET_T_EVENT_SENDER (only valid with EVENT_T_RECEIVE_AI_EVENT) to know who sent a received event

Note: This system is still in development, but this should already give many nice powers for first improvements and uses

Close cmangos/mangos-wotlk#110