license enum conversion

[jspaaks]

I may have an issue regarding licenses with converting from cff to zenodo. Both use a restricted vocabulary/enums for the license value, but cff uses SPDX while zenodo.json uses https://licenses.opendefinition.org/licenses/groups/all.json it seems. (needs confirmation)

specific problem occurs with license GPL-2.0-only (SPDX) v GPL-2.0 (opendefinition). on this repo/version: https://github.com/NLeSC/structure-from-motion/releases/tag/1.0.4. on zenodo the error is:

{
    "errors": "Unknown error occured."
}

[jspaaks]

related: schemaorg/suggestions-questions-brainstorming#251