Add total citation counts to library view when sort is by citation count

[aaccomazzi]

Not sure if this info is readily available from the solr response, but it would be nice to display the total number of citations for articles in a library when somebody wants it sorted by citations, the same way we do it for any search results. In fact, I don't see a reason why we should not display the total citations for any sort order.

There may be a reason why we can't get this for large libraries due to bigquery limitations, so this may need discussion.