In this commit several methods (child node add/remove and parent/root modification) were also moved to ve.dm.BranchNode ve.dm.Node respectively. ve.Node and ve.BranchNode are immutable. ve.dm.Node and ve.dm.BranchNode are mutable. Other subclasses of ve.Node and ve.BranchNode should implement functionality to mimic changes made to a data model.
Change-Id: Ia9ff78764f8f50f99fc8f9f9593657c0a0bf287e