Calculate cubemap coordinates in fragment shader

Fixes cubemaps being distorted
Ignore surfaces with non-special empty shaders
Loading plaque for Android
Rewrite that awful O(N*N) clients loop in G_PlayerAward
Mac fix
Draw loading plaque over purple screen
Let the UI check if certain graphics options are supported

Allow the UI to check if shadowmaps, soft particles, anisotropic
filtering and fullscreen are supported by GL so it can hide unsupported
graphics options
Remove shadowmaps from the prev commit because of RGB shadows