BibRecord: possibility to use lxml parser
BibRecord: possibility to use lxml parser

* Introduces and uses lxml when possible in BibRecord as well as outside
  in BibConvert, BibFormat, BibKnowledge and WebSearch.  (lxml is slower
  then rxp but faster than 4suite, so it is used in this preference order)

Co-authored-by: Tibor Simko <c7116e45300b163846dc01f3ed02116e3f8ef7a5@cern.ch>

tiborsimko/invenio-formatter,inveniosoftware/invenio-formatter,tiborsimko/invenio-formatter,tiborsimko/invenio-formatter,inveniosoftware/invenio-formatter,inveniosoftware/invenio-formatter