Include dc:extent in valid DC metadata

This PR makes two minor changes to the way that DC metadata is handled. The first is that it overrides the RDF properties that are included in the `descMetadata` datastream to include the dc:extent field which is required to import hte ksl:wrss collection. Any additional fields that are are required to be added to the application should be included here.

The second change is that the collection view now displays the dc:identifier (PID) field with the rest of the collections metadata.