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/Handler/IPayPalHandler.php

@@ -0,0 +1,20 @@
+<?php
+
+namespace PayPal\Handler;
+
+/**
+ * Interface IPayPalHandler
+ *
+ * @package PayPal\Handler
+ */
+interface IPayPalHandler
+{
+    /**
+     *
+     * @param \Paypal\Core\PayPalHttpConfig $httpConfig
+     * @param string $request
+     * @param mixed $options
+     * @return mixed
+     */
+    public function handle($httpConfig, $request, $options);
+}