Allow setting IPD manually + fixes

-r_oculusrift_ipd now can be used set an ipd between 0 and 100mm
-If r_oculusrift_ipd is set outside of that range (e.g., -1) it will
revert to the value provided by LibOVR
-r_oculusrift_prediction now reports the value set
-Moved hmd_settings_t definition inside oculus_sdk.c
-Magnetic drift correction now reenables after a orientation reset
-Magnetic drift correction now creates and deletes necessary resources
when enabled/disabled
-Eliminated extra math in R_InitHMDRenderer()
Prevent HUD from rolling when oculus sensors are reset
Don't roll the camera at player death when using an Oculus Rift