Need full namespace of PPOpenIdAddress, for PPModel magic to work.

When using PPOpenIdUserinfo:getUserinfo I get a PHP Fatal error:

"Class 'PPOpenIdAddress' not found in .... vendor/paypal/sdk-core-php/lib/PayPal/Common/PPModel.php on line 51"

That's because the PPModel magic that uses the method annotations can't instantiate a PPOpenIdAddress object without knowing its namespace.

This fixes that.