Utils: adds DOI json data fetching

* Adds JSON data response for a given DOI

* Adds etree to dictionary translation on processor utils

* Corrects get_marcxml_for_doi() misuse of plain text params
  in the url

* Needs the user's email as a configuration variable

Signed-off-by: Pedro Gaudêncio <pedro.gaudencio@cern.ch>
Reviewed-by: Javier Martin Montull <javier.martin.montull@cern.ch>
deposit: adds holding pen task for ongoing depositions

* This task adds the deposition to the Holding Pen so
  it gets approved or rejected by an administrator

Signed-off-by: Pedro Gaudêncio <pedro.gaudencio@cern.ch>
Reviewed-by: Javier Martin Montull <javier.martin.montull@cern.ch>
deposit: adds json api to fetch doi from crossref

* This searches the DOI on crossref and returns the result
  as JSON format, also handles if the DOI isn't found or
  it's malformed

Signed-off-by: Pedro Gaudêncio <pedro.gaudencio@cern.ch>
Reviewed-by: Javier Martin Montull <javier.martin.montull@cern.ch>