WIP: Position Tracking

Not quite working correctly yet..
TODO:
* need to adjust the position vector by the current head orientation
* add position reset using hot-key
* Warning if user leaves camera fustrum
Positional Tracking

Properly implemented this time. VRBoost Camera Translate can be used to
tweak the position.  F12 can be used to soft-reset the HMD orientation
and position
Pos Tracking Adjustment tweak

dividing by 100 meant that it took too long to make the camera move in
some games (bioshock)
Positional Tracking