BibTasklets: use bs4 instead of lxml

* Changes the way the fulltext XML is parsed from lxml.etree
  to bs4.BeautifulSoup to avoid errors with HTML5 entities that
  etree currently do not support.

* Improves submission feedback when running in devmode.

Signed-off-by: Jan Aage Lavik <jan.age.lavik@cern.ch>