* Clarified documentation related to drag & drop functionality in ITreeNodePresenter. * Removed FlagsAttribute from DragOperations. ** Updated related code for flag checking. * Implemented drop drop feature: allow PipingCalculation nodes to be dropped into any PipingCalculationGroup nodes. Related to Issue [WTI-174] git-svn-id: https://repos.deltares.nl/repos/WettelijkToetsInstrumentarium/trunk@1138 5a3db67b-de53-47b5-99c8-a1c30a6650e2