Manipulator-driven planar calibration

**Do this after #9 and #10**

A feature in New Scale's MPM Pathfinder is to touch the probe tip at 3 locations to define a plane and then level the atlas based on this plane. Implement this in Pinpoint. Allow the user to use a reference-coordinate-calibrated manipulator to touch three locations on the skull that should be the "level" surface, and use those three locations to define a plane. Then use the plane's transform (primarily rotation) as the root transformation and level the brain in Pinpoint.