About to make the Physics engine a view controller, not an NSObject. The goal is to marry the simulator to the view on which the simulated items are being displayed. I hope that this will help with: 1) converting coordinates, 2) removing the step of adding bubbles as subviews and adding them to the simulator, and others.

Also did some renaming of classes to the standard prefix of KB
1) Changed the physics sim to a view controller.
2) Client of sim can now set bounds on the view. Objects will deform when pushed against bounds.

Up next:
1) Changing drags so that they add a mass to a body, and the move drags the mass, thereby moving the body.
2) Velocities of bodies/masses so they keep moving when you stop dragging them.