Enemy Bullets and Camera Shake

-Enemies can now shoot (with all the same properties as players
shooting).
-Camera shake has been added and can be activated by any object with
camera access. The shake always uses the latest request and runs for 10
frames at the latest requested intensity.
-Simplified Physics layer interactions to exclude everything but what we
want.
-There was a weird bug with planets disappearing which was corrected by
deleting and readding them.