GtkStackSwitcher: More disconnect fixes
GtkStackSwitcher: More disconnect fixes

When resetting the stack, don't forget to disconnect signals.

https://bugzilla.gnome.org/show_bug.cgi?id=736307

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