Add source: OERBW/ZOERR
Based on https://gitlab.com/oersi/oersi-etl/-/blob/develop/data/to-oersibackend/oerbw-to-oersi.flux
But decided with @acka47 to use edu-sharing REST API here to evaluate it as an alternative to the embedded JSON-LD.
This might also provide a way to resolve #8 (closed), #9 (closed), and #10 (closed).