gtk-builder-tool: Handle cell properties
gtk-builder-tool: Handle cell properties

These were causing 'unknown property' warnings before.

alexlarsson/gtk,grubersjoe/adwaita,jadahl/gtk,Adamovskiy/gtk,alexlarsson/gtk,davidgumberg/gtk,davidgumberg/gtk,davidgumberg/gtk,chergert/gtk,davidgumberg/gtk,jadahl/gtk,jigpu/gtk,davidgumberg/gtk,chergert/gtk,jigpu/gtk,grubersjoe/adwaita,chergert/gtk,davidgumberg/gtk,alexlarsson/gtk,grubersjoe/adwaita,chergert/gtk,jigpu/gtk,Adamovskiy/gtk,jigpu/gtk,chergert/gtk,jadahl/gtk,Adamovskiy/gtk,chergert/gtk,Adamovskiy/gtk,grubersjoe/adwaita,jigpu/gtk,chergert/gtk,jadahl/gtk,grubersjoe/adwaita,davidgumberg/gtk,jadahl/gtk,alexlarsson/gtk,chergert/gtk,jigpu/gtk,grubersjoe/adwaita,Adamovskiy/gtk,grubersjoe/adwaita,alexlarsson/gtk,jadahl/gtk,Adamovskiy/gtk,jadahl/gtk,Adamovskiy/gtk,alexlarsson/gtk,grubersjoe/adwaita,jigpu/gtk,jigpu/gtk,jadahl/gtk,Adamovskiy/gtk,alexlarsson/gtk,alexlarsson/gtk,davidgumberg/gtk