Made GameObjects removeable by level by giving them an isDying method.
Made an object creator interface, which creates objects for the level. made turret one of these.
Added interactiveCollideable and objectCreator lists in level. interactiveCollidebales is now passed to collisionHandler.
Started a particleBeam class as a gameObject, which is not loaded using the usual constructor. Made a different constructor in gameObject for those not loaded from data.
Merged gameObject changes