fix to make sure nextFrameHandler callback is removed when a mesh is removed before any frame was actually rendered and this callback had no change to remove itself
implemented Unity-like forward rendering for the PhongEffect
fix Sprite init
re-implement the realistic material passes properly using the new PhongEffect interface
fix PhongEffect to properly push the _baseShader and _singlePassShader passes
move phong lighting specific "depth from light" shader parts into aerys.minko.render.shader.part.phong.depth
add ASDoc to explain the behavior of PhongEffect