dev/financial#33 Add in Hook alterIPNData to allow Extensions to do custom processing...

dev/financial#33 Add in Hook alterIPNData to allow Extensions to do custom processing of the IPN Data

Add in unit test of alterIPNData hook and ensure that it is called in all styles of IPN Notifications

Shift hook call to be done in handlePaymentMethod function as per Eileen's comment and remove the hook from deprecated pathways and passbyrefeence in hook

Change name to be postIPNProcess to be more explicit about the purpose of the hook