Change community syntax

The communities entry in the metadata seems to look a bit different on a downloaded entry than on the generated one: The generated one is [{"identifier": "escape2020"}] When looking at already existing entries: [{"id": "escape2020"}]

Examples for a already existing entry: https://zenodo.org/api/records/3362435

So maybe the "to be uploaded" format is different from the "downloadable" format? f that's the case, please reject this MR!

If that's the case, we should document that somewhere. WHere?

P.S.: The gitlab merge button often has an extra option to do a "fast forward" (or something like that). This avoids the merge commits in the history and makes git history nicer to look at.