Introduced StockChange. Implemented first part of stockit-logic with updating article's quantity.

test/fixtures/stock_changes.yml

@@ -0,0 +1,28 @@
+# == Schema Information
+# Schema version: 20090115232435
+#
+# Table name: stock_changes
+#
+#  id          :integer(4)      not null, primary key
+#  delivery_id :integer(4)
+#  order_id    :integer(4)
+#  article_id  :integer(4)
+#  quantity    :decimal(6, 2)   default(0.0)
+#  created_at  :datetime
+#
+
+# Read about fixtures at http://ar.rubyonrails.org/classes/Fixtures.html
+
+one:
+  delivery: 
+  order: 
+  article: 
+  quantity: 1
+  created_at: 2009-01-16 00:24:35
+
+two:
+  delivery: 
+  order: 
+  article: 
+  quantity: 1
+  created_at: 2009-01-16 00:24:35