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 uses David Herrmann's new logind sessions interface to retrieve
fds for input devices, rather than using a custom setuid helper to do
the management. This vastly simplifies the interface.
This requires systemd v210, at least.
https://bugzilla.gnome.org/show_bug.cgi?id=724604