Changes the node numberung for creation of VTK_WEDGE objects

VTK is inconsistent with numbering of 3D elements, especially when comparing QUAD and WEDGE elements (i.e. quad node numbering starts at the bottom of the element, wedge node numbering starts at the top). As a result prism elements have been rendered incorrectly until now in GUI since this is the only element where our node numbering differs from vtk node numbering. This PR fixes this "problem" which will result in correct rendering of prism elements even if backfaces are not rendered.