0022100: EDF 2413 SMESH: Take into account TRIA7

+  const SMDS_MeshNode* GetCentralNode(const SMDS_MeshNode* n1,
+                                      const SMDS_MeshNode* n2,
+                                      const SMDS_MeshNode* n3,
+                                      const SMDS_MeshNode* n12,
+                                      const SMDS_MeshNode* n23,
+                                      const SMDS_MeshNode* n31,
+                                      bool                 force3d);