Turn contest dashboard into tabs for easier navigation

config/routes.rb

@@ -18,7 +18,7 @@ Rails.application.routes.draw do
     resources :completions
     resources :contestants
     resources :puzzles
-    resources :messages, only: :destroy do
+    resources :messages, only: [ :destroy, :index ] do
       get "convert", to: "messages#convert"
     end
     get "import", to: "contestants#import"