Catch up on 1.6
This merge request updates the following, as they were updated in 1.6:
- wayland
- gtk3
- flatpak-xdg-utils
The branch also adds gsettings-desktop-schemas, which was added in 1.6.
Finally, this also updates appstream-glib, which is about to be updated in 1.6.
Edited by Mathieu Bridon