This allows us to use new Cogl APIs without having to define things in every .c/.h file manually.
Rework the radial effect to use similar code to MetaBackground, and adjust parameters to make it more noticeable. https://bugzilla.gnome.org/show_bug.cgi?id=725830
Use a new ShellGLSLQuad actor class to build a RadialEffect that can be enabled on Lightboxes to achieve a radial effect similar to the overview one. Then enable it for modal dialogs. https://bugzilla.gnome.org/show_bug.cgi?id=669798
