Disable Messagerie in archived Dossiers and procedures

* Use the existing Dossier#messagerie_available? method
* Raise when attempting to build a Commentaire if not messagerie_available?
* Disable the Messagerie form if not messagerie_available?
* Add tests :)
* Tweak the Horaires formatting while we’re here.

app/services/commentaire_service.rb

@@ -12,6 +12,9 @@ class CommentaireService
     end
 
     def build_with_email(email, dossier, params)
+      if !dossier.messagerie_available?
+        raise ArgumentError, "Commentaires cannot be added to brouillons or archived Dossiers"
+      end
       attributes = params.merge(email: email, dossier: dossier)
       Commentaire.new(attributes)
     end