Port from deprecated gtk_show_uri
requested to merge michaelweghorn/accerciser:michaelweghorn/port_from_deprecated_gtk_show_uri into master
Port from using the deprecated (in GTK 3.22) gtk_show_uri [1]
to the recommended alternative gtk_show_uri_on_window [2]
that takes a GtkWindow as first param instead of a GdkScreen.
[1] https://docs.gtk.org/gtk3/func.show_uri.html [2] https://docs.gtk.org/gtk3/func.show_uri_on_window.html