Implemention: Base gamma adjustment on the gamma ramps at startup

Because of changes in parameters for adjustment method function in both this patch and in the patch for full multi-monitor support this patch continues pull request #44 "Support for using any number of CRTC:s in any number of screens".

These two commits (the last in the list below; those made 2014-03-18) implements the feature suggested in
issue #32 "Base gamma adjustment on the gamma ramps at startup".