Add properties creator and contributor

public/instance/schema/shared-dc.rnc

 # Wiederverwendbare Definition von Eigenschaften aus Dublin Core Qualified
 #
 # Autor: David Maus <maus@hab.de>
-# Timestamp: <2019-01-16 12:22:25 maus>
+# Timestamp: <2019-01-16 12:27:31 maus>
 #
 
 namespace dct = "http://purl.org/dc/terms/"
@@ -9,6 +9,16 @@ namespace rdf = "http://www.w3.org/1999/02/22-rdf-syntax-ns#"
 namespace owl = "http://www.w3.org/2002/07/owl#"
 namespace skos = "http://www.w3.org/2004/02/skos/core#"
 
+property.creator =
+   element dct:creator {
+      entity.Agent
+   }
+
+property.contributor =
+   element dct:contributor {
+      entity.Agent
+   }
+
 property.identifier =
    element dct:identifier {
       model.rdfLiteral