Plugins Kinect2VAM - Full body tracking on the cheap

Fixes a bug that was disabling any active Possession mode when the 'Select None' button was clicked.

Registered the "Kinect Tracking On" toggle to make it available to triggers.

In order to preserve the integrity of any scene, the Person atom will no longer be teleported to World position 0,0,0 when the plugin is first loaded or calibration is reset. Instead the Person atom will just remain in the same pose and position, wherever they are located in the scene. It is now up to the user to determine how they then pose the Person atom prior to calibration. Obviously, the requirement to physically match that pose prior to calibration still remains.