standardise data dependencies

[casperdcl]

need consistent naming conventions

• have an equivalent of https://github.com/SyneRBI/SIRF-Exercises/blob/master/scripts/download_data.sh
  • potentially use https://github.com/TomographicImaging/CIL/blob/master/Wrappers/Python/cil/utilities/dataexample.py
  • NB: some zenodo zips have a top-level folder, some don't
  • NB: some zenodo zips need to be renamed post-extract (e.g. valnut -> Walnut)
  • NB: some zendodo files are not zips
• cleanup URLs
  • some notebooks mention the records (https://zenodo.org/records/NNNN), some mention filenames (https://zenodo.org/records/NNNN/files/XXX.EXT), some have cruft after the URL (#S0m3Hash?download=1)
• notebooks use different data paths... pick one
  • /mnt/materials/CIL
  • /mnt/materials/SIRF/Fully3D/CIL
  • ./samples/
• update all READMEs