Trackball fixes

Adding three features to the TrackballControls:
1.  Support for non-full window controls (by calculating the position of the cursor in the domElement
2.  Changing to use non-spherical trackballs for rotation (independent X/Y "radius")
3.  Making the "roll" on the outer edge of the trackball optional

I'm somewhat new to Javascript, but been doing OpenGL for a bit, so I'd appreciate any assistance in that department.