refextract: write references to timestamped file
refextract: write references to timestamped file

* Writes the xml lines from an extraction-job generated refextract task
  into a timestamped file, when the extraction has completed.

* Displays a message after an extraction-job has completed, printing the
  name of the output timestamped file.

* Adds garbage collection for refextract. Deletes only non-extraction-job
  output.

inspirehep/invenio-accounts,tiborsimko/invenio-accounts,inveniosoftware/invenio-accounts,inspirehep/invenio-accounts,tiborsimko/invenio-accounts,inveniosoftware/invenio-accounts,tiborsimko/invenio-accounts,inspirehep/invenio-accounts,inveniosoftware/invenio-accounts