GtkAboutDialog: Fix some focus issues
GtkAboutDialog: Fix some focus issues

Making a container focusable is rarely the right thing to do.
It typically breaks the focus chain, and makes the container
contents unfocusable, as was the case here.

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