ref #81 changed clicking behaviour:

left-click: replaces selection with clicked selection
ctrl + left: adds clicked selection to current selection
(or removes from current selection, if already selected)
right-click: removes complete selection
ref #81 improved synchronization between model picking/highlighting and treeview selection
ref #81 added checkboxes to sceneHierarchyTree to make nodes invisible/visible
ref #81 fixed PolygonalGeometry doesnt implement geometry() getter (but is declared in header file)