Review payment gateways

1.	Improve order reference mechanism so that external PG can assign real order number instead of guid		Closed	Denis Pavlov
2.	Refactor payment result page so that we can remove PG specific return pages		Closed	Denis Pavlov
3.	Review Authorize.NET PG		Closed	Denis Pavlov
4.	Review LiqPay PG		Closed	Denis Pavlov
5.	Review CyberSource PG		Closed	Denis Pavlov
6.	Review PayPal PG		Closed	Denis Pavlov
7.	Improve payment domain model to include taxAmount field		Closed	Denis Pavlov