treeview: Use drag gesture for rubberband selection/DnD
treeview: Use drag gesture for rubberband selection/DnD

This gesture acts only on events from the bin window, and checks that
either the pressed row is draggable, or the conditions for rubberband
selection apply.

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