Change hasPid cardinality to 0-1

[zozlak]

Currently the cardinality of acdh:hasPid is 0-n but having multiple would break all the services which depend on the acdh:hasPid being a primary resource identifier (most importantly the OAI-PMH service), therefore the cardinality should be set to 0-1

[bellerophons-pegasus]

The cardinality 0-n has the background that when creating the ontology, we thought that there might be cases where we end up with two identifiers, e.g. a Handle and some DOI, which should both be prominently presented.
But I think now with a few years in use it might be safe to say acdh:hasPid can only have one value and all others go into acdh:hasIdentifier.

Before doing that: please check if there is any entity in ARCHE that would violate the new cardinality constraint

[zozlak]

I confirm all existing resources have 0-1.