DLTP-227 File Thumbnail changes.

* The thumbnail/representative image on a work should be clickable and
  when clicked direct the user to the downloaded file for that
  representative file.
* On index page thumbnail should link to show page for curate concern.

dltp-227#

Fix file selection for link on thumbnail to representative image instead of just the first one.

Remove unnecessary line that was causing an error.

Fix one rspec test, add additonal rspec test for Article.

Correct extra tab spacing.