Introduced invoices and deliveries. Integration (especially of deliveries) isn't finished yet.

app/models/delivery.rb

@@ -0,0 +1,17 @@
+# == Schema Information
+# Schema version: 20090102171850
+#
+# Table name: deliveries
+#
+#  id           :integer(4)      not null, primary key
+#  supplier_id  :integer(4)
+#  delivered_on :date
+#  created_at   :datetime
+#
+
+class Delivery < ActiveRecord::Base
+
+  belongs_to :supplier
+
+  validates_presence_of :supplier_id
+end