Replace the ViewPort with a ViewDispatcher and an additional vertical
view. Both views use the same on_draw() and on_input() callbacks, as
they differ only in their orientation and name. Views are switched by
pressing the ok button.
The app is now left by a short back key press, because this is the only
way to invoke the navigation event handler of the view dispatcher. This
is also nice because there are no repeat or long press events which
would trigger a lot of view switches, as there is only a single short
press event per key press.