activity: Handle apps with "gnome-" prefix in their app ID
Otherwise we end up with "org.gnome.Gnome-software" kind of names.
This fixes missing icons in activity switcher for at least GNOME Calendar and GNOME Software.
Otherwise we end up with "org.gnome.Gnome-software" kind of names.
This fixes missing icons in activity switcher for at least GNOME Calendar and GNOME Software.