replace GL_MAX_TEXTURE_UNITS in favor of GL_MAX_TEXTURE_IMAGE_UNITS

GL_MAX_TEXTURE_UNITS is not relevant anymore as it represent the number of textures used for fixed pipeline multitexturing. GL_MAX_TEXTURE_IMAGE_UNITS is maybe more relevant but I think we should not rely on this to define how Rice should handle it's N64 texture units.
Finally totally remove the DecodedMux stuff and backport some hacks.
should fix (again) bad colors on textures for OGLES hardwares supporting BGRA (98%)
Add config option to force polygon offset values.

Provides a mechanism to workaround certain mobile hardware quirks.