f21, f22: Adapt for gtk3 / adwaita theming changes
    
    adwaita-gtk3-theme package is no more; gtk3 itself now includes the
    Adwaita theme. gnome-icon-theme and -symbolic were renamed to
    adwaita-icon-theme and merged together into one package, which is now
    pulled in by gtk3 package itself. adwaita-cursor-theme is gone too; the
    cursors are now included in the new adwaita-icon-theme package.