Add stock group order

This allows us to add additional items to an order, which do not belong
a specific user, but will be put into stock. The benefit of this change
is that we use the same order for ordergroups and stock.

app/views/orders/show.html.haml

@@ -70,6 +70,10 @@
     - if @order.open?
       = link_to t('.action_end'), finish_order_path(@order), method: :post, class: 'btn btn-success',
         data: {confirm: t('.confirm_end', order: @order.name)}
+      - if @order.stock_group_order
+        = link_to t('.stock_order'), edit_group_order_path(@order.stock_group_order, :order_id => @order.id), class: 'btn'
+      - else
+        = link_to t('.stock_order'), new_group_order_path(:order_id => @order.id, :stock_order => true), class: 'btn'
       = link_to t('ui.edit'), edit_order_path(@order), class: 'btn'
     - elsif not @order.closed? and not @order.stockit?
       = receive_button @order