This is a hybrid of None and Drop strategies.
Basically, if the puck is out of range for less then 1/2 a second we still use it, however any longer then that and we mark it as invalid.
Sitting and standing modes work even in desktop mode.
We were inadvertently checking for HMD Mode instead of if the head was valid.
* A change was made to the ViveControllerManager to return head poses in the correct standing universe when in desktop mode.
* The default sensorToWorld matrix in desktop mode is similar to the one returned by the system for Vive and Oculus sensor frame; y = 0 is at floor level.
* Sitting mode, walking mode and recentering flags are now visible in the AnimStats.
The openvr SDK provides a way to gauge the quality of tracking on a given device via the eTrackingResult enum.
* Drop - Only Running_OK is considered valid, all other eTrackingResults will return invalid poses.
* Freeze - Only Running_OK is considered valid, but other valid TrackingResults will return the last Running_OK pose.
In esseces this will freeze the puck in place at the last good value.
* None - All valid eTrackingResults will be valid, including OutOfRange and Calibrating results. This is the default.
* AnimInverseKinematics: debug draw for secondary targets
* AnimInverseKienmatics: better clean up of ik target debug draw
* GeometryUtil: added findPlaneFromPoints()
* ViveControllerManager: external dependency on eigen
* ViveControllerManager: record history of left/right hand controllers
* ViveControllerManager: use history to determine user shoulder location for better calibration
* ViveControllerManager: pass defaultToReferenceMat by const ref to calibrate functions.
* CMake: added external depenency to eigen linear algebra library.
* Fixed bug where head puck would sometimes not work properly when other vive trackers were enabled.
* Fixed calibration to work in sensor space instead of avatar space, this was necessary because
the sensor to world matrix is unreliable when in desktop mode.
