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/helpers/application_helper.rb

@@ -141,7 +141,7 @@ module ApplicationHelper
                               hint: 'The people responsible for the booth. You can only select existing users.'
   end
 
-  def event_types(conference)
+  def event_types_sentence(conference)
     conference.event_types.map { |et| et.title.pluralize }.to_sentence
   end