Moving game logic into a GameEngine class with new GameMoveableImage
interface.
Merge remote-tracking branch 'origin/master'

Conflicts:
	SpaceInvaders/src/GameFrame.java
	SpaceInvaders/src/GamePanel.java
	SpaceInvaders/src/Missile.java

Merged changes from Boris's earlier commits with mine... we had some
signficant overlap so I ended up just commenting out a fair amount.