We now not only load a texture's name, but also a thumbnail of the texture
itself, which we can show in the texview later, and from which we are going
to determine the material color to draw in the preview (note that the Color
field in .c4m files went away).
The code is not yet working properly, but it compiles
TODO: autotools build, material colors, Material&Texture overload,
relicensing, maybe algo=script