New function TraceLineToEntity()
Updates for crosshair

-Laser now stops on entities
-Depriciated r_oculusrift_crosshair 3
-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