Add PLOS cover images received 2014-10-09

These files don't overwrite the existing files - instead adopt PLOS' own naming conventions.
Rebuild PLOS journal cover markup for data package pages

Markup links to images from 2014-10-09 - wide and white background, replacing blue/green narrower (journal-sized) images.
Merge branch 'plos-covers' into dryad-dev
Merge pull request #750 from rnathanday/dryad-dev

Dryad dev PR #738