Add support for new texture formats
Previous changes removed LUMINANCE and ALPHA texture formats, and added R, RG, DEPTH_STENCIL, and DEPTH_FLOAT.
R and RG need to be correctly handed across different OpenGL versions. DEPTH_STENCIL and DEPTH_FLOAT need to be supported when extensions, etc. are present. There might need to be special work done to integrate them with FBOs as well.