Materials Project workflow data improvement

Fixes #663 (closed).

@mscheidg: I included a small script (nomad/cli/materials_project.py) for downloading and preparing an upload for the Materials Project data. If you think we should not include it yet, just tell me and I can take it away.

After this is merged and deployed to v1, I can upload a small dataset of 500 entries for starters. Before we upload more, we should really check the redistribution policy for the MP data and if we are doing the attributions correctly.