Break up the one-query-of-doom

The single query was producing a tremendously large ActiveRecord allocation.

While this isn't nearly as cool as one query, it's still a significant
reduction in SQL trips, and now has the bonus of only loading what is
actually going to be displayed.

app/views/conferences/_call_for_papers.haml

@@ -1,30 +1,27 @@
-- cache [conference, conference.call_for_events, conference.confirmed_tracks,
-  '#splash#callforpapers'] do
+- cache [conference_id, call, event_types, tracks, '#splash#callforpapers'] do
   .col-md-5.col-sm-5.text-center
     %h2
       Call for Papers
     %p.lead
       We are now accepting proposals for sessions!
     %p
-      - if conference.event_types.any?
+      - if event_types.any?
         You can submit proposals for
         %span.notranslate
-          = event_types(conference) + '.'
-      - if conference.confirmed_tracks.any?
+          = event_types.map(&:pluralize).to_sentence + '.'
+      - if tracks.any?
         Proposals should fit in one of the
         %span.notranslate
-          = pluralize(conference.confirmed_tracks.length, 'track') + ':'
-          = tracks(conference) + '.'
-      - if conference.call_for_events.try(:open?)
-        The submission period is open
-        %em.notranslate
-          = date_string(conference.call_for_events.start_date,
-            conference.call_for_events.end_date) + '.'
-        %b
-          You have
-          = pluralize(conference.call_for_events.remaining_days, 'day')
-          left!
+          = pluralize(tracks.length, 'track') + ':'
+          = tracks.to_sentence + '.'
+      The submission period is open
+      %em.notranslate
+        = date_string(call.start_date, call.end_date) + '.'
+      %b
+        You have
+        = pluralize(call.remaining_days, 'day')
+        left!
     %p.cta-button
       = link_to "Submit your proposal now",
-        conference_program_proposals_path(conference.short_title),
+        conference_program_proposals_path(conference_id),
         class: 'btn btn-success btn-lg text-center'