isajson: create @id for a number of ISA objects currently 'orphaned'

[proccaserra]

Background: Conversion from ISA-JSON to ISA-JSONLD and tuning of ISA JSON context files

• [ ] Person
• [ ] Publication
• [ ] FactorValue
• [ ] Characteristics(Value)
• [ ] ParameterValue
• [ ] OntologyAnnotation
• [ ] OntologySource

Affected component: isajson.py

example fix on def get_ontology_source(obj) (https://github.com/ISA-tools/isa-api/blob/0e934efcc32b13166a3808ec3373116078e47912/isatools/isajson.py#L1599) return clean_nulls( { "@id": id_gen(obj), "name": obj.name, "description": obj.description, "file": obj.file, "version": obj.version, "comments": get_comments(obj.comments) if obj.comments else [] }

[proccaserra]

further testing indicates retrofit is needed for the following objects too

• [ ] investigation
• [ ] study
• [ ] assay