Log Message:
Update gnome-desktop3 to 3.16.2

- Drop libgsystem dependency (#680326)
- Modernize gtk-doc use (#742479)
- Fix memory handling in GnomeRR and language code (#742111, #742569)
- Fix mutex handling in thumbnailing code (#740666)
- Fix thumbnailing failures due to internal cleanups (#684026)
- Add installed tests (#737140)
- Recognize builtin monitors in Dell machines (#740289)
- Improve thumbnail handling (#684026)
- languages: Use a more broadly compatible locale codeset suffix (#710412)
- Remove unused code in gtk-reftest (#737123)
- Translation updates