elsevier_package: Reworks adding of affiliations

* Adding of affiliations now works in 3 stages
    * Referenced affiliations are added
    * Affiliations in the same author_group are added if there
      were no referenced affiliations
    * Affiliations of higher hierarchies are added

* Check "Tag by Tag The Elsevier DTD 5 Family of XML DTDs" for
  more information.

Signed-off-by: Martin Vesper <martin.vesper@cern.ch>
NLM & JATS: fix for extracting authors in colaborations

* Fixes extracting authors when "contrib" tag is used to indicate a
  collaboration. To avoid having fake author with all affiliations we
  skip "contrib" tag with "contrib" subtags.
Merge pull request #87 from Dziolas/nlm_autor_fix

NLM & JATS: fix for extracting authors in collaborations
Merge pull request #83 from mvesper/missing_affiliations

elsevier_package: Reworks adding of affiliations
installation: setup Travis CI

Signed-off-by: Jan Aage Lavik <jan.age.lavik@cern.ch>
MiniDOM_utils: remove striping commas from xml_to_text function.