Use URI of bank account on payments form

To complete a payment, we need to use URI.
Checkout payment on PaymentsController#create
Debit a bank account through Payment class
Use UID to refer to bank accounts

IDs can't be used to make a debit.
Create PaymentGenerator class to define need of delay payments
Add some line breaks
Checkout using Payment class when able to debit resource
Use DelayedPayment class when the account can't be instantly debited
Defines checkout of DelayedPayment
Remove shared_examples from context

This behavior of Rspec is deprecated.
Expect use of PaymentsGenerator on PaymentsController

The use of Payment and DelayedPayment is internal of Generator. Should
not be expected when using PaymentGenerator.
Merge pull request #31 from neighborly/im-delayed-payments

Delayed Payments
Merge pull request #26 from neighborly/im-checkout-payment

Checkout payment when completing a contribution