Update the show action for the shopping cart controller to use solr queries to grab the solr responses for all shopping cart item ids + the ids of those items' parents.
Committing because I need to blow up my VM.
Update test to account for sorting of core records and download items.
Update the solr_document_behavior to have a method that will, assuming an object with a 'content' datastream, return the label on that datastream.  Useful for getting filenames out of content objects.
Update the view logic to use SolrDocuments constructed from solr queries.
change sort_by to sort_by! so sorting actually occurs (woops).  Update comments to clarify rationale for sorting.
Merge pull request #373 from nu-lts/feature/solrized_download_queue_lookup

Feature/solrized download queue lookup