DeclarativeObserver: Removed the SubcomponentEditorTool

DeclarativeObserver: Removed the SubcomponentEditorTool

This tool made selecting items in your QML app more complicated than
necessary. Now, left-click will always just select the top-most item
under the mouse and right-click will allow you to select any of the
items below.

Also, the highlighted bounding rect now always applies to just one
item, instead of also including the children bounding rect.

Reviewed-by: Kai Koehne
Change-Id: I17b5ab397d951fd68711590469ca6e723a9cb0e6
(cherry picked from commit 73060143c30d38ea99e6d7a77ff81c94f58899d7)