Support for multiple technical metadata records

Hi Scape

This is my fork of the scape data model. I have made a few minor changes to, like making a common superclass (Identified) for IntellectualEntity, Representation, File and Bitstream. There are a few changes so the converter outputs correct METS, as the METS was not valid before.

The big change was making the Technical Metadata record in Representation, File and Bitstream into a List, rather than a single entry. This allows us to store the metadata we actually need in the objects. The tests have been updated and a test using multiple metadata records have been added