Updated Payment APIs

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

lib/PayPal/Api/PaymentHistory.php

@@ -3,16 +3,15 @@
 namespace PayPal\Api;
 
 use PayPal\Common\PayPalModel;
-use PayPal\Rest\ApiContext;
 
 /**
  * Class PaymentHistory
  *
- * A list of Payment Resources
+ * List of Payments made by the seller.
  *
  * @package PayPal\Api
  *
- * @property \PayPal\Api\Payment payments
+ * @property \PayPal\Api\Payment[] payments
  * @property int count
  * @property string next_id
  */
@@ -20,9 +19,8 @@ class PaymentHistory extends PayPalModel
 {
     /**
      * A list of Payment resources
-     * 
      *
-     * @param \PayPal\Api\Payment $payments
+     * @param \PayPal\Api\Payment[] $payments
      * 
      * @return $this
      */
@@ -42,9 +40,38 @@ class PaymentHistory extends PayPalModel
         return $this->payments;
     }
 
+    /**
+     * Append Payments to the list.
+     *
+     * @param \PayPal\Api\Payment $payment
+     * @return $this
+     */
+    public function addPayment($payment)
+    {
+        if (!$this->getPayments()) {
+            return $this->setPayments(array($payment));
+        } else {
+            return $this->setPayments(
+                array_merge($this->getPayments(), array($payment))
+            );
+        }
+    }
+
+    /**
+     * Remove Payments from the list.
+     *
+     * @param \PayPal\Api\Payment $payment
+     * @return $this
+     */
+    public function removePayment($payment)
+    {
+        return $this->setPayments(
+            array_diff($this->getPayments(), array($payment))
+        );
+    }
+
     /**
      * Number of items returned in each range of results. Note that the last results range could have fewer items than the requested number of items.
-     * 
      *
      * @param int $count
      * 
@@ -68,7 +95,6 @@ class PaymentHistory extends PayPalModel
 
     /**
      * Identifier of the next element to get the next range of results.
-     * 
      *
      * @param string $next_id
      *