Remove the old MetaMonitorConfig system and mark the new one as non-experimental. This also removes the D-Bus property. https://bugzilla.gnome.org/show_bug.cgi?id=777732
It'll be used elsewhere, so shouldn't be in MetaMonitorManagerKms. https://bugzilla.gnome.org/show_bug.cgi?id=777732
Introduce MetaSettings and add the settings managed by MetaBackend into the new object. These settings include: experimental-features and UI scaling factor. https://bugzilla.gnome.org/show_bug.cgi?id=777732
