widget-factory: Demonstrate listbox headers
widget-factory: Demonstrate listbox headers

Add a less trivial examples of headers in the colors listbox.

ahodesuka/gtk,jessevdk/gtk,jessevdk/gtk,davidgumberg/gtk,grubersjoe/adwaita,jadahl/gtk,Adamovskiy/gtk,Lyude/gtk-,jigpu/gtk,Adamovskiy/gtk,davidgumberg/gtk,jadahl/gtk,Lyude/gtk-,grubersjoe/adwaita,jigpu/gtk,alexlarsson/gtk,davidgumberg/gtk,davidgumberg/gtk,jessevdk/gtk,jadahl/gtk,jadahl/gtk,grubersjoe/adwaita,alexlarsson/gtk,alexlarsson/gtk,davidgumberg/gtk,alexlarsson/gtk,Adamovskiy/gtk,Lyude/gtk-,grubersjoe/adwaita,ahodesuka/gtk,jessevdk/gtk,alexlarsson/gtk,chergert/gtk,davidgumberg/gtk,chergert/gtk,grubersjoe/adwaita,Adamovskiy/gtk,jadahl/gtk,ahodesuka/gtk,ahodesuka/gtk,chergert/gtk,Adamovskiy/gtk,Adamovskiy/gtk,Lyude/gtk-,grubersjoe/adwaita,alexlarsson/gtk,chergert/gtk,ahodesuka/gtk,jessevdk/gtk,jessevdk/gtk,Lyude/gtk-,Adamovskiy/gtk,jigpu/gtk,Adamovskiy/gtk,jessevdk/gtk,ahodesuka/gtk,jadahl/gtk,alexlarsson/gtk,jigpu/gtk,chergert/gtk,jigpu/gtk,ahodesuka/gtk,Lyude/gtk-,jigpu/gtk,chergert/gtk,chergert/gtk,grubersjoe/adwaita,jigpu/gtk,Lyude/gtk-,ahodesuka/gtk,davidgumberg/gtk,Lyude/gtk-,chergert/gtk,alexlarsson/gtk,davidgumberg/gtk,jadahl/gtk,grubersjoe/adwaita,jadahl/gtk,jigpu/gtk