scalebutton: Handle smooth scroll events
scalebutton: Handle smooth scroll events

This has the double effect to make scale button truly smooth, and make
scrolling work on wayland, since all scrolling is "smooth" there.

https://bugzilla.gnome.org/show_bug.cgi?id=720269

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