Support transformation to JSKOS concordance

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Requires source and target come from fixed vocabularies. This can be checked automatically, either by passing concept schemes in JSKOS or by calculating a common namespace (maybe also based on curie_map).

[nichtich]

With option --schemes it's possible to add inScheme to all concepts. If schemes match on subjects and objects, respectively, the result can be a made a JSKOS concordance.