!97 added a do not disturb switch to GNOME Shell. This works by
changing the org.gnome.desktop.notifications.show-banners setting.
The switch that controls this setting in the control center should
therefore use the same Do Not Disturb label as the switch in the
shell.
Switch from GtkBuilder to using GtkTemplate.
Rename widget IDs to be more readable.
Drop widget IDs that are not used.
Move code into the .ui file that can be.
Connect signals in swapped form.