Add all currently-available aggregations

** Why are these changes being introduced:

This app implements only two filter / aggregation categories: content
type and source. However, others are now supported by the API:
Contributors, format, languages, literary form, and subjects. Others are
coming soon, but for now these are what is available.

** Relevant ticket(s):

* https://mitlibraries.atlassian.net/browse/gdt-128

** How does this address that need:

This updates our search model, and filter helper, to add support for the
new categories.

** Document any side effects to this change:

Because all queries now include this request for more aggregations, we
need to regenerate a number of the test cassettes.

Author: matt-bernhardt

app/helpers/filter_helper.rb

@@ -22,7 +22,12 @@ def add_filter(query, filter, term)
   def nice_labels
     {
       contentTypeFilter: 'Content type',
-      sourceFilter: 'Source'
+      contributorsFilter: 'Contributor',
+      formatFilter: 'Format',
+      languagesFilter: 'Language',
+      literaryFormFilter: 'Literary form',
+      sourceFilter: 'Source',
+      subjectsFilter: 'Subject'
     }
   end
 

app/models/timdex_search.rb

@@ -60,10 +60,30 @@ class TimdexSearch < TimdexBase
             key
             docCount
           }
+          contributors {
+            key
+            docCount
+          }
+          format {
+            key
+            docCount
+          }
+          languages {
+            key
+            docCount
+          }
+          literaryForm {
+            key
+            docCount
+          }
           source {
             key
             docCount
           }
+          subjects {
+            key
+            docCount
+          }
         }
       }
     }