[VTK] Missing biquadratic element - 9 noded quads

[jginternational]

Description
When using biquadratic quadrilaterals, (9-nodes) Kratos can not find the element for VTK.

  File "E:\GiD\GiD 16.1.6d\scripts\tohil\python\lib\site-packages\KratosMultiphysics\vtk_output_process.py", line 67, in PrintOutput
    self.vtk_io.PrintOutput()
RuntimeError: Error: Modelpart contains elements or conditions with geometries for which no VTK-output is implemented!
Cell type: 10

I've seen in https://github.com/KratosMultiphysics/Kratos/blob/master/kratos/input_output/vtk_definition.cpp that we have not defined this element for VTK, that corresponds to VTK_BIQUADRATIC_QUAD, cell type 28 in:
https://kitware.github.io/vtk-js/api/Common_DataModel_CellTypes.html