Remove redunant code from the renderer and make things more generic (sic)
This moves all the render pipelines that have been class members into a std::map so that we can iterate over them, this makes it a lot easier to get rid of some code duplication.
It also introduces a FileReader class which is only used for now to read the shader code. Before that, that same code was on the renderer itself since the beginnings of (OLives) times, where it obviously did not belong.