This is an implementation of the pad OSD that's been previously
present in gnome-settings-daemon. Since things are moving closer
to the compositor, it makes sense to have this implemented as shell
UI.
https://bugzilla.gnome.org/show_bug.cgi?id=771067
Display notifications that have not been dismissed in the message
list - eventually this will replace the existing message tray summary.
Notification messages show icon, title and one line of the body and
can be clicked to activate the default action. However they cannot be
expanded, so other actions or the full body text are not accessible
in this mode.
https://bugzilla.gnome.org/show_bug.cgi?id=744817
The message list is a scrollable list that will hold sections of
different types of time-related messages like notifications,
calendar events or birthday reminders. When no section displays
any content for the selected date, a placeholder is shown instead.
https://bugzilla.gnome.org/show_bug.cgi?id=744817
