Zenodo uploader new features

[alastair]

When I ran the uploader for 2019 I ran into these issues:

• If the ee field pointed to archives.ismir.net, it didn't correctly download the files in order to upload them to zenodo. I worked around this by adding a local path to the files in this field when running the uploader
• The uploader replaces the ee field with a link to zenodo, however: 1) this link doesn't actually seem to work, 2) for consistency perhaps we want to keep this on archives.ismir.net?
• If we have additional data (e.g., an "extra" key that we added to 2019 for takeaway message/external links) then the updated data file that the uploader writes doesn't include these keys