Explosion on object destruction.
Some bugs fixed.
Ufo enemy added.
Some changes in world model classes structure.
Merge branch 'master' of https://github.com/jczarnowski/SpaceShooter
Collision detection moved to EntityHandler.
New class ScreenGrid for collision handling inprovement.
Lots of small changes.
new gun kind
new gun kind - rest of prev commit
Merge branch 'master' of https://github.com/jczarnowski/SpaceShooter

Conflicts:
	src/com/jcf/spaceshooter/engine/Assets.java