API: GnomeRR: replace direct XRandR calls with DBus calls to mutter

Mutter now provides a DBus API that wraps XRandR and abstracts
away the detail of running X or wayland.

A number of API changes are needed, as GnomeRR is no longer in
charge of maintaining the monitors.xml file updated.

https://bugzilla.gnome.org/show_bug.cgi?id=705510
GnomeRR: restore support for gamma ramps

The color panel of control center needs it.

Note: the color panel and color g-s-d plugins will have different
changes for wayland support, but they still need the code in the
XRandR case.

https://bugzilla.gnome.org/show_bug.cgi?id=705510
GnomeRR: restore support for raw EDID access

The color plugin of gnome-settings-daemon needs it to build
the default ICC profile for uncalibrated displays.

https://bugzilla.gnome.org/show_bug.cgi?id=705510
GnomeRR: fix gnome-rr-debug test case

Use GnomeRR facilities to read the EDID instead of direct X access,
because the actual XID is not exposed in the API (although it is
exported on the bus)