Select nested zone in indicator

[gerritdevriese]

From #75

Allow selecting a specific zone from any of the layout boxes when you have zone overlay active: With the zone overlay, you have to move the window to/near the zone you want to move to. If you're on one end of the screen on an ultrawide, that's a long distance the mouse has to go. Instead, when you show the overlay, if you could go to the closest layout box and then select a zone in that layout box, that would mean less mouse travel. I can explain more if this is confusing.