Add the FramebufferSelection class.

No support for direct rendering (rendering with no post shaders) yet.
GLSLProgram and Material Selection classes.
Shared default Material.
Uniform warning fixup.
Push material down to the GeometryNode.
Set evinronment map in RenderingContext::sync.
Add a separate depthRender method in GraphNode.
MaterialSelection::getSelectedShaders()
Restore PostOverlay-less rendering.