Removed Collideable interface, pretty much every sprite needs to be
compared at some point so i moved collision detection code into the
Sprite class.

Also, InputMaster gets linked as a keylistener on both the Frame and the
GLCanvas in it, until now, every time you switched focus to a different
window and switched back to space invaders, key events wouldn't be
processed, now the singleton should always get events regardless of what
you clicked on to get focus back.
Changed Collision detection code to use new collision size instead of
using the sprite itself as the collision model, offset now applies only
to the final drawn sprite, you cannot offset collision.

Also added health and score variables.
You can now spawn a wave of bad guys with W / Up Arrow! Bad Guys move
down in a zig-zag pattern towards the ground, are disposed of when
health hits 0, and speed up and get more health with every wave spawned.

Also hard-coded in stats for the player actor, considering leaving a
public static reference to current Drawable object updated with every
call to a GLEvent in SpriteMaster...