rewrite handleAdd to produce valid dataQuads

currently, only BlankNodes or empty string Literals are produced as quad objects by handleAdd but this should depend on either a sh:nodeKind constraint and/or further constraints (eg. sh:class => BlankNode, sh:datatype => Literal).

Example:

At https://roger.bdn-edition.de/ chose the shape "Werk Shape".

Add an entry for "Autor".