timeline: Support notification whenever surface changed its title for forcing object refresh
A piece left for the timeline part is to signal (from shell, by calling
weston_timeline_refresh_subscription_objects()) whenever the surface title has changed. It appears that the notification for that has to happen through the shell (but there doesn't seem to be any listeners for that?).
I had a tentative to fix it: !233 (8ee186a8), but it is not correct.