SlicerCAT error with hdf5

PR is ready
It builds HDF5 as external project that is used by both VTK and ITK

@fbordignon I wanted to point out to you that VTK8 support has now been removed from latest Slicer. I know you’ve been piecing together older Slicer with newer Python and other mixing of new and old stuff. Did you get around to updating your application to use latest version of Slicer? There won’t be maintenance of Slicer 4 branches now that Slicer 5 is officially released and available to download.