Added exclusive OverrideTraceScreenRay() for ZoomTilt (which is immune t...

...o ground height variation)

-also add zoom boundary around map for Non-freemode option
-renamed some Global constant variable (cleanup thing)
-also, had to remove ZoomTilt's Horizon check because not compatible with zooming into water (y<0). Still work!
readded GetGroundHeight here because this portion do not effect ZoomTilt