systemd-lock-handler: print message before starting mainloop
systemd-lock-handler: use o.f.l.Manager.GetSession()
systemd-lock-handler: print message when locking
systemd-lock-handler: kscreenlocker is gone, call org.fdo.ScreenSaver

The use of 'gdbus' here is temporary.
systemd-lock-handler: some restructuring
systemd-lock-handler: implement DBus method