Renaming Namespaces and Organizing Classes

- Updated OpenId classes to be in API namespace
- Updated PP Naming Convention to PayPal Naming Convention
- FormatConverter Class got its own namespace
- Handlers are grouped in Handler namespace
- Samples and Tests Updated Accordingly

lib/PayPal/Api/Notification.php

@@ -2,7 +2,7 @@
 
 namespace PayPal\Api;
 
-use PayPal\Common\PPModel;
+use PayPal\Common\PayPalModel;
 
 /**
  * Class Notification
@@ -15,7 +15,7 @@ use PayPal\Common\PPModel;
  * @property string note
  * @property bool send_to_merchant
  */
-class Notification extends PPModel
+class Notification extends PayPalModel
 {
     /**
      * Subject of the notification.