NumerableIcon.setBackgroundGicon

Updates the icon to use icon as the base background image. If icon is null, self will go back using style information or default theming for its background image.

If this method is called and an icon name was already set as background for the icon, icon will be used, i.e. the last method called between [gtk.numerable_icon.NumerableIcon.setBackgroundGicon] and [gtk.numerable_icon.NumerableIcon.setBackgroundIconName] has always priority.