AI script hooks and on_damaged callback

[Grokmoo]

(1) The AI script should have the ability to specify callback functions just like an ability script can now. So that the AI can register a function to be called on attack, on defense, etc.

(2) Create an on_damaged callback that calls every time the parent is damaged, should include the attack information like on_defense does now. Should be callable from AI and ability scripts.

[Grokmoo]

Resolved by 1e068ae