Just removed a comment that said there was something wrong with the
heading.
DevicePose: changed getHeadnig() to return the heading in degrees and
not radians, to be consistent (degrees all throughout).
PointDouble: Added methods calculateRadiansTo(PointDouble other) and
add(offsetX, offsetY):PointDouble.
Made getDeviceCoords() public.
Corrected the testWithBadINSGoodVINS() method. Too simple though. Will
improve it next time by re-observing a feature (accurately) more times.