Add primary clipboard persistence
Follows apps/mousepad!3 (closed).
Closes #31 (closed).
Related upstream issue: https://gitlab.gnome.org/GNOME/gtk/-/issues/317
This adds a setting to make primary clipboard persistent over deselection, at the desktop level rather than at the application level, as discussed in apps/mousepad!3 (closed), since it seems that this will never be added in GTK+ (see this comment of the maintainer in particular).
Edited by Gaël Bonithon