elsevier_package: adds missing year in references.

Signed-off by: Georgios Papoutsakis <georgios.papoutsakis@cern.ch>
Merge pull request #23 from GiorgosPa/elsevier

elsevier_package: adds missing year in references.
springer_crawler: adds new module

* to crawl from Springer web pages.

Signed-off by: Georgios Papoutsakis <georgios.papoutsakis@cern.ch>