Fix LookAt

Also have player use generic LookAt and offload the transform into the
controller
Add method to get the center position of a sprite
Vector2 add was doing subtraction
Spawn bullets from crosshair position
Import and variable cleanup
Do a bit of work to reformat and javadoc ImagesLoader
Fix removing bullets from the world when colliding with enemies
Rework how visibility of actors is managed

Also add notification of when actors are added to the world
Notify actors of newly added enemies

Bullets also now stop when colliding with bricks
Fix bullet setting
Removing and cleaning up debug and
Merge branch 'master' into AI
Change world to use Sets instead of ArrayLists for representing actors
Also fix errors that got reverted
Have Actors respond with a slight stun and animation when hit
Remove the excess check on bullets, now they should we working properly