Merge branch 'bernd/tet_splitting' into 'master'

Tet splitting

`Refinement - Split to Tets` works now for me with this change.
I'm unsure, if this introduces any other bugs.

See merge request !3

libsrc/meshing/meshclass.cpp

@@ -4099,6 +4099,8 @@ namespace netgen
         UpdateTopology();
         timestamp = NextTimeStamp();
       }
+
+    RebuildSurfaceElementLists();
   }
 
   void Mesh :: BuildElementSearchTree ()
@@ -5070,7 +5072,6 @@ namespace netgen
     static int timer = NgProfiler::CreateTimer ("GetSurfaceElementsOfFace");
     NgProfiler::RegionTimer reg (timer);
 
-
      /*
      sei.SetSize (0);
      for (SurfaceElementIndex i = 0; i < GetNSE(); i++)