Use rdfs:label instead of schema:name in JSON-LD representing resources

[benjamingeer]

Following the discussion in #620 about schema.org and the responses to schemaorg/schemaorg#1762, I suggest that we not use schema.org entities in the current API v2 ontology schemas, because it seems that the software that actually uses those entities is designed to understand only those entities. Instead, we could take @subotic's suggestion and consider making a schema.org Knora ontology schema that would be designed to work with that software.