default result sorting to quiz submission descending

completes #85

app/controllers/admin/result_controller.rb

@@ -10,7 +10,9 @@ module Admin
 
     # TODO: Limit results to the quizzes current_user has access to
     def index
-      @candidates = Candidate.where(completed: true).includes(:recruiter)
+      @candidates = Candidate.where(completed: true)
+                             .includes(:recruiter)
+                             .order(:review_status, completed_at: :desc)
     end
 
     def view