Preserve license

[elichad]

Adds limited preservation of license to the Zenodo metadata.

Notes:

• legacy Zenodo API accepts only an id for the license, which is the same as the license's SPDX identifier, but lowercase.
• you can search the Zenodo license list using id, name, URLs, etc, but this is very unreliable if there are multiple licenses with similar names/ids. I tried to implement this, but I couldn't get the number of false matches down far enough for some of the common licenses.
• due to these limitations, the code will only be able to set the license if the RO-Crate license @id is the SPDX URI for that license. Other URIs, names, etc. will not work.