The order and way include macros were structured was chaotic, with no
real common thread between files. Try to tidy up the mess with some
common scheme, to make things look less messy.
This basically moves g-s-d's orientation plugin into mutter so that
eventually g-s-d doesn't need to build monitor configurations by
itself anymore.
https://bugzilla.gnome.org/show_bug.cgi?id=781906