/moderator/dashboard: optimize sql queries

* Converts queries to use active record instead of raw sql. This ensures
  that user objects are loaded by rails in the join, so that we
  don't have to issue `User.find` calls to load users one-by-one.

* Use `.includes` to preload associations used in the view, to avoid
  additional N+1 query problems (primarily, calls to link_to_user
  also causing users to be loaded one-by-one).

app/logical/moderator/dashboard/queries/user_feedback.rb

@@ -3,7 +3,7 @@ module Moderator
     module Queries
       class UserFeedback
         def self.all
-          ::UserFeedback.order("id desc").limit(10)
+          ::UserFeedback.includes(:user).order("id desc").limit(10)
         end
       end
     end