bibrecord: improve handling of record parser
bibrecord: improve handling of record parser

* The MARCXML record parser will now be handle XML hierarchy depths
  beyond subfields. I.e. any HTML content inside subfield values
  will be stripped, but their content kept.

tiborsimko/invenio,tiborsimko/invenio,inveniosoftware/invenio,inveniosoftware/invenio