DVDVideoCodec: Add static methods to hide / enable / query user settings
VDPAU: Remove AdvancedSettings for mpeg4
VDPAU: Add Expert Settings to let user easily disable certain codecs
VAAPI: Remove Mpeg4 Advanced Setting
VAAPI: Make Codec selection an expert setting (disable mpeg4, vc1 by default)
Settings: Add description and examples to the new settings
Settings: Use new Codec Settings function to hide settings for nvidia users