Add actor event "slots" for standard interaction

[VectorWolf]

If something like a colission between actors happens, a specified event could be triggered

• Possible slots:

  • on_collide
  • on_activation
  • on_hit
  • on_death

• As a result we need an "add_cause" method which adds a pointer to the actor which triggered the event.

• For pointer consistency the actors in the actor layer should be stored in lists rather than vectors.

• Events which use this "cause" functionality should always have a nullptr case.