Make concept scheme URI and CURIE-prefix for vocabulary independent from each other

[dalito]

This issue is inherited from vocexcel.

VocExcel always uses the concept scheme URI to define a prefix named "cs". The prefixes defined in the "Prefix sheet" in Excel do not at all influence the generated turtle output. They are only used to convert all CURIEs used in Excel to URIs.

This default behavior is not nice for URIs like https://w3id.org/nfdi4cat/voc4cat_0123456 (OBO style). With a concept scheme URI of https://w3id.org/nfdi4cat/voc4cat all CURIES have an underscore in them cs:_0123456. To make the CURIEs nicer (cs:0123456) the concept scheme URI could be defined to have a trailing underscore (https://w3id.org/nfdi4cat/voc4cat_), but this is also uncommon and could lead to confusion.

Desired behavior:

• Do not automatically use the concept scheme IRI to define a prefix "cs" used in rdf/turtle.
• Use a per-vocabulary defined prefix. In voc4cat we can use idranges.toml to set this preferred prefix.