Don't allow changes to settled orders (PR #614)

app/views/finance/balancing/_edit_results_by_articles.html.haml

@@ -11,7 +11,7 @@
       %th= heading_helper Article, :deposit
       %th{:colspan => "2"}
         = link_to t('.add_article'), new_order_order_article_path(@order), remote: true,
-          class: 'btn btn-small'
+          class: 'btn btn-small' unless @order.closed?
   %tbody#result_table
     - for order_article in @articles
       = render :partial => "order_article_result", :locals => {:order_article => order_article}