ENH: Add support for model hierarchies in subject hierarchy

Handled cases:

Scene changes

1. Hierarchy node added
   -> Add folder item
   ( folderPlugin::addNodeToSubjectHierarchy )

2. New parent is set to a hierarchy node
   (Modified event for both old and new parents)
   newParent.vtkMRMLHierarchyNode::ChildNodeAddedEvent(hierarchyNode)
   -> Set parent of item for hierarchy node to item for new parent
   ( folderPlugin::onMRMLHierarchyNodeChildNodeAdded )

3. Scene import ends
   -> Add each hierarchy node to subject hierarchy and resolve hierarchy on each added item
   ( addSupportedDataNodesToSubjectHierarchy,
   folderPlugin::addNodeToSubjectHierarchy,
   resolveHierarchyForItem )

4. Data node is associated to a hierarchy node
   dataNode.vtkMRMLNode::HierarchyModifiedEvent
   (Should only happen if building hierarchy programmaticaly from scratch)
   Remove hierarchy node's item from subject hierarchy
   ( folderPlugin::onDataNodeAssociatedToHierarchyNode )

Subject hierarchy changes

1. Item is reparented under an item with node hierarchy
   1a. New parent has associated hierarchy node
   -> Set parent item's hierarchy node as parent of reparented item's hierarchy node
   ( folderPlugin::reparentItemInsideSubjectHierarchy )
   1b. Otherwise
   -> Set scene as parent of reparented item's hierarchy node
   ( folderPlugin::reparentItemInsideSubjectHierarchy )

git-svn-id: http://svn.slicer.org/Slicer4/trunk@25753 3bd1e089-480b-0410-8dfb-8563597acbee