Added check to make orientation calculations more robust

Added check avoid a division by zero resulting in NaN which in turn
makes checkFullyTilted to ignore high tilt angles from then on.
If (x, y, z) == (0, 0, 0) then there is no tilt or rotation and
this vector must be ignored. This check is extended to ignore all
small acceleration values where noise can be of big influence.

Low or zero readings can happen when space travelling free falling,
but more commonly when shaking or getting bad readings from the sensor.
The accelerometer is turned off when not used and polling it too soon
after it is turned on may result in (0, 0, 0).

Change-Id: I19aec653abb8ab6f7126778035c8c96449f1326f