DAM-303: Renaming Rockhall::Pbcore to Rockhall::Exports
DAM-303: Export pbocre, solr and discovery xml documents via new dropdown
minor change
Tidying-up next and previous navigation links
Tidying up user navbar

Delete button moved to Edit menu
DAM-303: Adjusting test
Ignoring nil or empty dates
DAM-234: Adding title_sort field; enabling collection_facet