Add support for icons in menus.
Add support for icons in menus.

sharoonthomas/gtk-mac-integration,sharoonthomas/gtk-mac-integration,jralls/gtk-mac-integration,sharoonthomas/gtk-mac-integration,jralls/gtk-mac-integration,jralls/gtk-mac-integration,sharoonthomas/gtk-mac-integration,GNOME/gtk-mac-integration,GNOME/gtk-mac-integration,sharoonthomas/gtk-mac-integration,GNOME/gtk-mac-integration