Solidified the Rotation Vector sensor on Android and it now remaps to the correct coordinate system based on the device orientation.  Tested with 4 different devices (2 phones, 2 tablets) and they all work as expected.  Fixed copy/paste typo that causes sensors to never be disabled on Android.  Added Gravity sensor on Android, which can be used, amongst other things, to flip the Rotation sensor coordinates if a devices has been flipped.