* remove calculating as a checkout status (making it separate)
* include checkout is calculating for determining whether to flip payment status to process
* only change payment method state for status changes if needed
* fix reducer for shipping state
* include checkoutIsCalculating for determining whether to show validation errors in checkout block
* change where currentStatus is defined
* fix bug with saved payment method option
* Add saved-payment-method options handling and improve payment method registration initialization
* add server side exposure of saved customer payment methods
* fix reducer for express payment method state
* fix default for customerPaymentMethods
Darren Ethier