bibcheck: Adds first implementation

* Adds first implementation of chk_fix_bad_elsevier_affiliations,
  which is a use-once plugin to re-add the existing affiliations
  using the sa:affiliation field

Signed-off-by: Martin Vesper <martin.vesper@cern.ch>
Merge pull request #26 from mvesper/bad_affiliation_plugin

bibcheck: Adds first implementation