GNOME 3.32 icon name changes

The following GNOME 3.32 app were released after UI Freeze (with no previous 3.31 releases) with a different app icon name.

- preferences-desktop-font → org.gnome.font-viewer
- gnome-characters → org.gnome.Characters
- applets-screenshooter → org.gnome.Screenshot

Except for gnome-screenshot, these releases also adapt to the new GNOME menu guidelines so I think we do need to do these updates.

Without the proposed change, those applications will appear with GNOME upstream icons, instead of the Yaru ones, this is why I consider this a UI Freeze exception.

This change is addressed adding new symlinks between the new and the old icon names, without removing the latters, so that the risk of regression issues is really low, if not zero

 - if any of the applications above should appear with the old icon name, the old symlink will provide the correct icon name
 - if any of the applications above should appear with an icon name different than the old or the new, upstream icon will be used anyway as it would be without this change

Finally, the change has been tested installing the affected applications from [[https://launchpad.net/~jbicha/+archive/ubuntu/temp332/+packages|here]]