GtkAssistant: Redo page margins
GtkAssistant: Redo page margins

Instead of having padding outside the notebook containing
all pages, put each page in an extra box and add the padding
there. This is in preparation for allowing pages without
padding.

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