Smarter event area assignment

[stasgora]

Current state

Currently the innermost Detector always catches the interaction. There are cases when an additional Detector has to be placed due to a scrollable list but the current content does not overflow the widget area.

Solution

Every Detector that handles a scrollable area should be able to detect if there is currently any content overflow. If not there is no need to process that area in separation and the event should propagate to the Detector higher up the tree.