Some fixes for the crosshair

* Laser now stops on entities as well as walls
* Depriciated r_oculusrift_crosshair 3 since it didn't make sense to have as an entire separate mode.
* Implemented r_oculusrift_crosshair_depth to allow manually specifying depth for crosshair. Default is zero, and all settings <= 0 trace to the first wall.
* Switched the crosshair size calculation to use screen width instead of height to make it less sensitive to aspect ratio