Add "passthrough" commands to dui::item::config

[ebengoechea]

As pointed by @Damian-AU, dui::item::config doesn't take the same set of arguments as the dui widget creation command, e.g. -label_fill, -outline, etc. when the widget is a "dui compound". Althoug tag conventions allow to configure each part, it would be more usable if the same set of arguments could be used.