MyAvatar: refactored updateFromHMDSensorMatrix() a bit by splitting it into several methods, because
it was getting quite large and becoming hard to follow.
* beginStraighteningLean() - can be called when we would like to trigger a re-centering action.
* shouldBeginStraighteningLean() - contains some of the logic to decide if we should begin a re-centering action.
for now it encapulates the capsule check.
* processStraighteningLean() - performs the actual re-centering calculation.
New code was added to MyAvatar::updateFromHMDSensorMatrix() to trigger re-centering when the avatar speed rises
over a threshold.
Secondly the Rig::computeMotionAnimationState() state machine for animGraph added a state change hysteresis
of 100ms. This hysteresis should help smooth over two issues.
1) When the delta position is 0, because the physics timestep was not evaluated.
2) During re-centering due to desired motion, the avatar velocity can fluctuate causing undesired animation state fluctuation.
Now triggers 7 states.
Idle, WalkFwd, WalkBwd, StrafeLeft, StrafeRight, TurnLeft & TurnRight.
As well as variable speed walking to match current velocity.
