EDM: Preserve metadata hierarchies (hasPart)

[twagoo]

EDM records may be 'metadata parents' having e.g.

<dcterms:hasPart 
  xmlns:dcterms="http://purl.org/dc/terms/"
  rdf:resource="http://data.theeuropeanlibrary.org/BibliographicResource/3000051827382"/>

or they may be 'metadata children' having e.g.

<dcterms:isPartOf 
  xmlns:dcterms="http://purl.org/dc/terms/"
  rdf:resource="http://data.theeuropeanlibrary.org/BibliographicResource/3000053640021"/>

Preserve this information in the generated CMDI by creating metadata type resource proxies in the parent record.