REFAC: Camera now provides projection allowing picking, RbdPlaneToSphereCDExample now uses picking

Just some imstk free time fun!

iMSTK should have been including the projection matrix in the camera. Now it does! Allowing picking!

Checkout usage in RbdPlaneToSphereCDExample. Pick up a sphere, click, hold and drag to fling it around.

Also, a getter for window size in the Viewer.