Model Renderer|GL: Ambient light in the model shader
libgui|GLBuffer|GLProgram: Added a fourth set of texture bounds
libgui|ModelDrawable: Emission and specular maps

The emission map is simply added to the shader output. Specular map
RGB control specular reflection color and intensity, while specular
alpha determines the dullness/sharpness of the highlight.

Todo: Refactor and clean up.
Model Renderer|GL: Trying out the emission and specular maps

Todo: Refactor and clean up.