Added some options to RigidBody to create Rigid Bodies which can't rotate or move
Added the ObjMan class which will be managing rigid bodies and resolving their collisions
Also added a little testing code; not enough to really be sure that it works, but enough
testing so that I know it's not totally fucked up.
improved the testing for collision resolution by adding two walls to the simulation and another
block.  Also added code to ObjMan to zero out a rigid body's velocity after a collision; later
this will be replaced by actual impulse calculations