Use types from the triplestore in predicate objects in ontologies

[benjamingeer]

The case class PredicateInfoV2 stores the objects of predicates of ontology entities. Currently, PredicateInfoV2 stores all its objects as strings. When ontology information is converted from one schema to another, objects that are actually IRIs have to be converted. Since PredicateInfoV2 doesn't know the types of its objects, something else has to keep track of that. So there are hard-coded sets of predicates that are known to have IRIs as objects, but this is cumbersome. It also means that to convert an IRI, PredicateInfoV2 needs to convert a string to a SmartIri and back again.

This PR takes advantage of the type information that comes with SparqlExtendedConstructResponse to enable PredicateInfoV2 to store store IRIs as SmartIri objects instead of strings.

• Add a trait OntologyLiteralV2, which is like LiteralV2 but has just the implementations needed by PredicateInfoV2. (OntologyLiteralV2 shares some of its implementations with LiteralV2.)
• Refactor PredicateInfoV2 to use OntologyLiteralV2.
• Use a Seq instead of a Set for the objects in PredicateInfoV2, so a Seq[StringLiteralV2] can be accepted as a Seq[OntologyLiteralV2] (this doesn't work with Set, because Set is not covariant in its type parameter).
• Fix bug: when API v2 served knora-api (default schema), salsah-gui:guiElement and salsah-gui:guiAttribute were not shown in properties in that ontology.
• Fix bug: salsah-gui:guiOrder was not accepted when creating a property via API v2.

As a result, PredicateInfoV2.toOntologySchema becomes nice and simple:

def toOntologySchema(targetSchema: OntologySchema): PredicateInfoV2 = {
    copy(
        predicateIri = predicateIri.toOntologySchema(targetSchema),
        objects = objects.map {
            case smartIriLiteral: SmartIriLiteralV2 => smartIriLiteral.toOntologySchema(targetSchema)
            case other => other
        }
    )
}

Resolves #738.

[subotic]

LGTM, thanks :-)

[benjamingeer]

Thanks for the review!

[subotic]

you shouldn't work on a Saturday ;-)

[benjamingeer]

Neither should you. :)