Bug fixes for Snapdragon2D; Added collision detection

-Fixed NPE in GammaTable
-Implemented (and moved) CollisionModel (not yet tested!)
-Implemented remaining Entity methods/fields
-Added rectangle collision detection to World2D
-Changes to PointLD
-Added builds directory

CollisionModel has NOT YET BEEN TESTED.  It may or may not work right
now... testing and udpates will be pushed to the next commit.
Removed '.classpath'