0022100: EDF 2413 SMESH: Take into account TRIA7

0022100: EDF 2413 SMESH: Take into account TRIA7

Now  SMDS_VtkCellIteratorToUNV inherits from SMDS_NodeIterator and
hence next() returns a node

-class SMDS_VtkCellIteratorToUNV: public SMDS_VtkCellIterator
+class SMDS_VtkCellIteratorToUNV: public SMDS_NodeIterator, protected SMDS_VtkCellIterator
 {
 public:
   SMDS_VtkCellIteratorToUNV(SMDS_Mesh* mesh, int vtkCellId, SMDSAbs_EntityType aType);
+  virtual const SMDS_MeshNode* next();
+  virtual bool more();
   virtual ~SMDS_VtkCellIteratorToUNV();
 };