Make it possible for panels to go all the way to the edge of the
shell. This is particularly important for panels that scroll, such
as the new power panel. All other panels are changed to compensate
for the loss of external padding.
https://bugzilla.gnome.org/show_bug.cgi?id=691229
Show applications using the message tray, and
allow configuring in what way the shell presents them.
The set of applications shown include all applications that ever
showed a notification in gnome-shell and all applications that have
a boolean X-GNOME-UsesNotifications key set to true in their desktop file.
https://bugzilla.gnome.org/show_bug.cgi?id=685928
