Modified Crosswalk definition to match Importer expectation

applications/registry/core/libraries/importer.php expects a crosswalk
to have a validate($payload) method - see line 874 of that file.
Importer expects crosswalk to have metadataFormat()
Merge pull request #1 from DigitalCurationCentre/crosswalks

Modified Crosswalk definition to match Importer expectation