Add base/null prefix to be SPHN in the SPHN Ontology case

In the 2022 Ontology (and before) the null/base prefix has been the ontology. We used this in the shacler to generate pseudo prefixes for the Shape Names. If we have no null prefix then the shapes for the SPHN Shacl have prefixed-IRIs like "constraint:sphnAllergy" instead of "constraint:Allergy".

This is what needs to be added in the ttl:

@prefix : <https://biomedit.ch/rdf/sphn-ontology/sphn#> .

For a project specific ontology it should be different then.