Got rid of all GL.Enable (EnableCap.ColorMaterial) calls !

Got rid of all GL.Enable (EnableCap.ColorMaterial) calls (which were
really painful due to expensive GL.Material calls that had to be done in
addition). Instead, using generated 1x1 pixel size coloured textures for
non-Thumbnailed files.
Also using mipmaps for thumbnailed files - better quality for minified
textures.
All nodes are now unified - all using textures - code cleanup due to
this was possible.