Reimplemented depth textures and added getters for the textures of the framebuffer.
Changed some attributes of the scene class to make it easier to override.
Repaired texture generation parameters for full OpenGL ES 3.0 compatibility.
Changed depth texture rendering to use the default framebuffer texture for depth.
Added a preprocessing scene class to make postprocessing easy to do. Also added a simple depth and normal scene and a texture to full screen quad scene to aid in the implementation of light pre pass.