Allow selecting parent widget for arrow target

[lassoan]

We need a way to select the arrow to point to any of the parent widget of a widget. For example, I may want to draw an arrow to the entire toolbar not to a specific toolbar button. We could use for example the mouse wheel or a right-click menu to choose the widget or any of its parents. To make it clear what widget is selected, show a (temporary) frame around the selected widget or parent.

[vmms]

Added a new feature to select the parent widget using scroll.