Print info about missing required cvars for various settings

[VReaperV]

Some of the settings we have, like specular maps and reflection maps require one or more other settings to work. The engine should inform one about such missing settings, which is currently done only for static reflections, and with a very ambiguous message at that.

Ideally, this should also be reflected in graphics settings, like disabling some setting automatically and showing a text saying "requires .. setting".