contrast_out: adds MissingTagException to _get_text_from_journal_item

* adds MissingTagException and a brief description to _get_text_from
  _journal_item

* does some general code cleanup

Signed-off-by: Martin Vesper <martin.vesper@cern.ch>
elsevier_package: fixes unpack bug of get_publication_information

* does some general code cleanup

Signed-off-by: Martin Vesper <martin.vesper@cern.ch>
scoap3utils: adds MissingTagException

Signed-off-by: Martin Vesper <martin.vesper@cern.ch>