Entities and classes for tracking payments

PolicyCenter uses the following Gosu objects and data model entities to track the usage of payment instruments and payments for a policy period:

Item	Type	Usage
`PolicyPeriodBilling InstructionsManager`	Gosu object	Tracks the payments that the selected payment plan requires and the up-front payments that the user enters.
`BillingPayment InstrumentImpl`	Gosu object	Provides basic information about each payment instrument for a policy. The billing system is the system of record for these payment instruments. The PolicyPeriodBillingInstructionsManager object uses these objects in communication with both an external payment system and an external payment gateway.
`TokenizedCreditCard Details`	Gosu object	Provides two `String` values. One value, which typically has a format similar to `xxxx-1234`, identifies a credit card on the Payment user interface. The other value is a token that identifies the card to the payment gateway.
`PaymentInformationBase`	Gosu object	Transfers information about a payment to the payment gateway for processing.
`PaymentGateway Transaction`	Data model entity	Associates an up-front payment request with a PolicyPeriod entity instance. PolicyCenter deletes the PaymentGatewayTransaction entity instance when it receives confirmation that the payment gateway has processed the payment.
`PaymentGatewayResponse Base`	Gosu object	Contains the information that a payment gateway returns from a request that PolicyCenter makes.
`PaymentGatewayResponse Processor`	Gosu object	Processes the information in a PaymentGatewayResponseBase object for the PolicyPeriodBillingInstructionsManager object.
`UpFrontPayment`	Data model entity	Stores an up-front payment for a job. The PaymentGatewayResponseProcessor object creates this entity for an up-front payment on receiving a successful response from the payment gateway.