Second part of stock-integration.

Introduced StockArticle and a special page for ordering from stock. StockChanges will be created and the StockArticle.quantity
updated in 'order.close!'.

app/models/supplier.rb

@@ -26,6 +26,7 @@ class Supplier < ActiveRecord::Base
 
   has_many :articles, :dependent => :destroy,
     :include => [:article_category], :order => 'article_categories.name, articles.name'
+  has_many :stock_articles
   has_many :orders
   has_many :deliveries
   has_many :invoices