Attack system on rabbits, no item drops yet

@PimV, @sagar193, @jhay 

needed to work around an crash, for some reason the killed rabbit isn't properly removed for the list.
That's why the respawn looks so odd.
Als je toch een setter/getter maakt, kan je hier net zo goed ff valideren of de nieuwe healthpoints wel kloppen? (dus iets van: if (healthPoints < 0) this->healthpoints = 0;