DOC: Update the Gitlab banner to new VTK logo design.
DOC: Update the Gitlab banner to new VTK logo design.

Thanks to Steve Jordan, the VTK new logos are now available at:
https://www.vtk.org/download/

lorensen/VTKExamples,lorensen/VTKExamples,lorensen/VTKExamples,lorensen/VTKExamples,lorensen/VTKExamples,lorensen/VTKExamples,lorensen/VTKExamples