Click-cycle order should start with closest object

Since the number of slack pixels has been increased, it is often possible to select an object which is further away from the mouse than the one you intended to click on.

We need to construct a list of objects sorted by range from the mouse position, and be careful to cycle through that list in order.

We may need a heuristic to ensure that if the mouse is moved away from its previous position (or the list changes), we reset the search order.