Post Processing

[Gallasko]

Add a post processing step to the render to be able to apply filter or postprocessing effects to a frame
For this we need to change the current rendering steps and add:

1. Binding of a FBO to be able to render the frame as a texture instead of directly in screen
2. Render all the object as we are currently doing
3. Generate the texture from the FBO once all the object are renderered for this frame
4. Unbind FBO -> Render to screen the generated texture using the postprocessing shaders