treeview: Use gestures for column dragging/resizing
treeview: Use gestures for column dragging/resizing

A multipress gesture takes care of autosizing on double click, and
a drag gesture is used for both column dragging/resizing (only one
can happen at a time).

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