Support search for resources owned by one of multiple organisations

See #246

Deployed to staging, see:

http://staging.api.lobid.org/resource?id=TT001352973&owner=DE-107,DE-1018 (only owned by DE-107)
http://staging.api.lobid.org/resource?id=HT013126064&owner=DE-107,DE-1018 (only owned by DE-1018)

@ahagenbruch Does this work for your use case?

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