Scale down oversize icons in menus (Bugs 10545, 10461)

Use exo_gdk_pixbuf_scale_down to ensure the icons in the menu don't
exceed the selected icon size.
I18n: Update translation sr (100%).

216 translated messages.

Transifex (https://www.transifex.com/projects/p/xfce/).
I18n: Update translation uk (100%).

216 translated messages.

Transifex (https://www.transifex.com/projects/p/xfce/).
Updates for release.
Post release tag bump.