Decrease lag generated by autorotation on

There are different issues from what I understand:

1) Discarding of events too close to each others is broken
as mAccelerationTimestampNanos is conditionned by isAccelerating()
on TF101 no events are discarded anymore, and so it creates an update every ~50ms
filing up the android notification message queue quite a bit for nothing and so generating lag.
2) isAccelerating seems incorrect to me too, the code means more that it's accelerating "out of range" and should be discarded in that case.

=> Discard the sample if outOfRange and don't condition the update of mAccelerationTimestampNanos that way next time we come back "too soon"
the sample will be properly discarded.

3) with events being discarded properly on the WindowOrientationListener
the SensorManager can now update every 20ms instead of 50ms
but that is definitely overkill.
=> add SystemProperty sensor.loop.minms with a default value of 50ms to throttle the notifications.
That way the thread sleeps properly instead of sending events as fast as it can.

(increasing up to 100ms can be ok depending if you want faster response or not.)
This can be positionned on a per device prop too.

4) Add 2 SystemProperties:
one on the SystemSensor side: sensor.magnitude.threshold with a default 0 value(doesn't change the behavior)
one on the WindowOrientationListener: orientation.magnitude.threshold with a 200 (0.2G) default value
These allows to discard the sample if it is too close to STANDARD_GRAVITY (ie not accelerating much)
These can be set on a per device or use the default values.
On the TF101 200 works most of the time. But weirdly when docked the reported gravity seems to have an additionnal offsert of -0.2
maybe some magnetic interference from the dock...

For the moment the 0.2G threshold is positionned on the Orientation code.
Once the cpp sensor poll crazy loop is solved it could be better to use the sensor.magnitude.threshold instead.

That should take care of most of the lag generated by autorotation.

Change-Id: I093227f539050a6bad8e6e8d9f533eff7bddd0d6