UI: Disable the "Color Depth" option when full screen mode is disabled

[kai-li-wop]

The Color Depth option in the Graphics menu should be grayed out, i.e. displayed as disabled, and set to Default when Full Screen mode is disabled. So far, 16bit or 32bit can be selected in windowed mode and also applied via Accept with a restart. However, as long as WoP is operated in window mode, this remains practically without effect, since automatically the color depth of the desktop is taken over, even if not indicated in the menu. ioquake3 has already implemented a solution for this.

[mgerhardy]

should be fixed

[kai-li-wop]

It is tested and considered fixed!