added density, friction and restitution to Rectangle.js
Added step call to update method in PhysicsSystem.js
Merge branch 'master' into Justin
Created physics world in scene.  fixed syntax of some box2d calls
Merged logic of two box2d components into one Physics component
Added get/set methods for fields of the physics component.
Merge branch 'master', remote-tracking branch 'origin' into Justin
Added add circle method to PhysicsSystem.js
Added init method to PhysicsSystem.js edited update method
added impulse/force methods
Merge branch 'master', remote-tracking branch 'origin' into Justin
fixed bugs started working in scene
Getting things ready for project 2 code submission
Cleaning up more code