Improved system for post processing shaders.

This is the system for improving configurability of shaders from a user perspective.

This doesn't have multiple render stages in the PP shader backend, but is more centered towards bringing configurations of the shaders options to the UI.
Good question.
For the argument if it is "" it loads the shader from the global videocommon active config object, otherwise loads the shader given.
The argument passed to it is the shader name, eg "FXAA".
So it loads the shader from the userdirectory + argument + ".glsl"

The return is the actual shader source after it's done loading the shader + configurations.