Add ship cannon
Changes for recent engine changes. Add another test ship.
Create Bullets projectile source
Add IDamageSink to support world objects that take damage. Implement interface for Ship. Bullets now inflict damage when they hit an IDamageSink. There is a slight issue with collisions being in both directions. The bullet inflicts damage when it hits a ship, but the ship also detects a collision with anything in the world (eg ground) and takes damage too. This means bullets cause two sets of damage. To limit this particle mass default is set really low so that a) particles by default don't nudge the thing they hit much and b) they don't inflict damage on any body.