Extend mappings during import

[nichtich]

• When fromScheme is given (or inferred from concordance), all member concepts in from should get field inScheme unless already existing
• When toScheme is given (or inferred from concordance), all member concepts in to should get field inScheme unless already existing

Mismatch of fromScheme and inScheme does not need to be tested, as this is better done as part of validation library.

[nichtich]

I'm not sure whether this is required, needs further investigation why current import does not work as expected.

[stefandesu]

This has never been a thing. Concept objects in mappings don't usually have field inScheme at all because it can be inferred from fromScheme/toScheme.