open-with-widget: add support for fallback applications
open-with-widget: add support for fallback applications

Needs some new API in GIO, which is not yet merged.

jessevdk/gtk,jadahl/gtk,Adamovskiy/gtk,Sidnioulz/SandboxGtk,jessevdk/gtk,chergert/gtk,simokivimaki/gtk,ebassi/gtk,davidt/gtk,chergert/gtk,Distrotech/gtk2,davidt/gtk,ahodesuka/gtk,davidgumberg/gtk,Sidnioulz/SandboxGtk,davidgumberg/gtk,jessevdk/gtk,grubersjoe/adwaita,chergert/gtk,davidgumberg/gtk,bratsche/gtk-,ahodesuka/gtk,simokivimaki/gtk,jadahl/gtk,jigpu/gtk,jadahl/gtk,bratsche/gtk-,davidt/gtk,msteinert/gtk,msteinert/gtk,alexlarsson/gtk,bratsche/gtk-,Adamovskiy/gtk,chergert/gtk,jessevdk/gtk,chergert/gtk,jigpu/gtk,davidgumberg/gtk,bratsche/gtk-,Lyude/gtk-,ebassi/gtk,jigpu/gtk,alexlarsson/gtk,grubersjoe/adwaita,grubersjoe/adwaita,jessevdk/gtk,jessevdk/gtk,ebassi/gtk,jessevdk/gtk,Distrotech/gtk2,Distrotech/gtk2,alexlarsson/gtk,jigpu/gtk,grubersjoe/adwaita,ahodesuka/gtk,ahodesuka/gtk,Lyude/gtk-,Distrotech/gtk2,Lyude/gtk-,grubersjoe/adwaita,Distrotech/gtk2,msteinert/gtk,chergert/gtk,davidgumberg/gtk,Sidnioulz/SandboxGtk,davidgumberg/gtk,jadahl/gtk,Sidnioulz/SandboxGtk,simokivimaki/gtk,Sidnioulz/SandboxGtk,alexlarsson/gtk,alexlarsson/gtk,alexlarsson/gtk,simokivimaki/gtk,davidt/gtk,grubersjoe/adwaita,jadahl/gtk,ebassi/gtk,ebassi/gtk,davidgumberg/gtk,Sidnioulz/SandboxGtk,bratsche/gtk-,grubersjoe/adwaita,jigpu/gtk,Lyude/gtk-,Adamovskiy/gtk,msteinert/gtk,Lyude/gtk-,Adamovskiy/gtk,Distrotech/gtk2,Adamovskiy/gtk,simokivimaki/gtk,Adamovskiy/gtk,jigpu/gtk,Lyude/gtk-,msteinert/gtk,ahodesuka/gtk,ahodesuka/gtk,bratsche/gtk-,simokivimaki/gtk,grubersjoe/adwaita,jadahl/gtk,Adamovskiy/gtk,jadahl/gtk,davidt/gtk,Lyude/gtk-,ahodesuka/gtk,jadahl/gtk,davidt/gtk,alexlarsson/gtk,jigpu/gtk,Lyude/gtk-,ahodesuka/gtk,chergert/gtk,Adamovskiy/gtk,msteinert/gtk,jigpu/gtk,ebassi/gtk,alexlarsson/gtk,chergert/gtk,davidgumberg/gtk