Sensor: Add RotationVectorSensor2

Some ICS apps (namely, Google Maps) expects a rotation vector to be
available. Newer devices, this is provided by either Android's
sensor fusion (requires Gyro) or by hardware sensor fusion (MPL).

Older devices will lack this virtual sensor and compass in Google
Maps will not work. To fix this, we can provide our own rotation
vector sensor by converting the values from the orientation sensor.
(They are basically the same information in different formats.)

Thanks to Unhelpful for the help with related math.

Change-Id: I596f5dc44f8797bc280ae5d1e110bb92387c79d1