For easier binding and introspectability, rework GnomeRRConfig and
GnomeOutputInfo to be GObjects (GInitables, actually) instead of
boxed types. This commit *does* break API, as previous API just
accessed fields in the public structs, while now everything has been
moved to private structures and accessors must be used.
Also, rework GnomeRRLabeler to use both a public and a private structure,
so that gobject-introspection can find instance/class sizes.
Modifications to gnome-control-center and gnome-settings-daemon will
follow.

https://bugzilla.gnome.org/show_bug.cgi?id=630913