Integrates blacklight-citeproc gem into application.

[bwatson78]

1. Gemfile*: adds and incorporates needed gem and it's dependencies.
2. citation_controller.rb: overrides and refactors gem's original controller because
   error was occuring when attempting to print multiple bookmarks' citations.
3. catalog_controller.rb: institutes the configuration for the citation gem into the catalog controller.
4. solr_document.rb: allows the extension of Bibtex into a solr_document.
5. print_multiple.html.erb: creates a unique view for printing multiple citations, so that
   space may be incorporated in between each document's citation.
6. print_single.html.erb: overrides the gem's default in order to display the citations with appropriate styling.
7. routes.rb: removes the gem's routes and, instead, points to the refactored/retooled controller listed above.

[bwatson78]

[bwatson78]