orcidutils: better Orcidpush papers detailed info

* Corrects the way how external-ids were obtained.
* Improves publication date retrieval.

Signed-off-by: Mateusz Susik <mateusz.susik@cern.ch>
Reviewed-by: Samuele Kaplun <samuele.kaplun@cern.ch>
Reviewed-by: Jan Aage Lavik <jan.age.lavik@cern.ch>
Merge branch 'inspire-invenio/pr/123' into prod