Turn contest dashboard into tabs for easier navigation

config/locales/en.yml

@@ -260,6 +260,8 @@ en:
     none: No field selected
     rank: Rank
   messages:
+    index:
+      no_messages: No messages received yet
     convert:
       title: New completion
     destroy:

config/locales/fr.yml

@@ -231,6 +231,8 @@ fr:
     none: Aucun champ sélectionné
     rank: Rang
   messages:
+    index:
+      no_messages: Pas de messages reçus pour le moment
     convert:
       title: Ajout d'une complétion
     destroy:

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"