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

tests/PayPal/Test/Api/CurrencyTest.php

@@ -2,8 +2,8 @@
 
 namespace PayPal\Test\Api;
 
-use PayPal\Common\PPModel;
-use PayPal\Common\FormatConverter;
+use PayPal\Common\PayPalModel;
+use PayPal\Converter\FormatConverter;
 use PayPal\Validation\NumericValidator;
 use PayPal\Api\Currency;