Action class to handle the redirected request from PayPal following a PayPal
Express Checkout session in which the user's address and payment information
are defined directly with PayPal.
When PayPal redirects the user back to the application, this class triggers
the second of the three API calls of PayPal Express,
GetExpressCheckoutDetails, to retrieve the details of the user's interaction
with PayPal Express on the PayPal website.
The execute method of this class invokes
, or whatever class is defined in the "activePaymentProcessors" setting that
corresponds to the paypalExpressForm.jsp template, to communicate with