Slide down from top border to exit fullscreen
To exist fullscreen apps from a touch scren in GNOME, we have to slide down from the top border. It has been decided to implement this behavior in GNOME Shell rather than to implement that in each and every app, see https://gitlab.gnome.org/GNOME/epiphany/issues/814 for context.
we likely should implement the same in Phosh. What do you think, @tobias.bernard?