Always produce simple literals from strings, not always xsd:strings.

git-svn-id: https://svn.apache.org/repos/asf/jena/trunk@1564937 13f79535-47bb-0310-9956-ffa450edef68
Enable as many JSON-LD tests as possible.

git-svn-id: https://svn.apache.org/repos/asf/jena/trunk@1564938 13f79535-47bb-0310-9956-ffa450edef68