Renderer|VR: Eye offset applied to the eye origin (for clipping etc.)

Also refactored the model view matrix function to be somewhat clearer.
Menu|All Games: Added "Reset Tracking" in the Controls menu
Oculus Rift|Renderer: Prevent cheating by peeking through surfaces

In Oculus Rift (head tracked) mode, putting one's head physically
through walls and planes results in a black screen.

Todo for later: The blanking out should occur at near clip distance.