Shader Viewer Update

I really like the new shader viewer; it really makes editing shaders and viewing them on different models fast. However, when it comes to your own shaders, it really needs an option to load up textures for mtlskin1-3 if your shader uses it. As right now, it just takes in account the skins contained in the model file and shows the mtl skins as black.

Ok, we'll add an option to load material skins in a future version.