Updated Payment APIs

- Updated SDK Models to latest Payment APIs
- Updated Unit Tests

lib/PayPal/Api/NameValuePair.php

@@ -3,7 +3,6 @@
 namespace PayPal\Api;
 
 use PayPal\Common\PayPalModel;
-use PayPal\Rest\ApiContext;
 
 /**
  * Class NameValuePair
@@ -19,7 +18,6 @@ class NameValuePair extends PayPalModel
 {
     /**
      * Key for the name value pair.  The value name types should be correlated 
-     * 
      *
      * @param string $name
      * 
@@ -43,7 +41,6 @@ class NameValuePair extends PayPalModel
 
     /**
      * Value for the name value pair.
-     * 
      *
      * @param string $value
      *