Bibtasklets: adapts tasklets to changes in Harvesting kit

* Refexctract and knowledge bases handling is now done in
  the tasklets.

Signed-off-by: Georgios Papoutsakis <georgios.papoutsakis@cern.ch>
Merge pull request #46 from GiorgosPa/refextract

Bibtasklets: adapts tasklets to changes in Harvesting kit