refactored IPN to use base IPN class from civicrm

This allows use of webhook in format /civicrm/payment/ipn/N

https://github.com/drastik/com.drastikbydesign.stripe/issues/221

CRM/Core/Payment/Stripe.php

@@ -912,4 +912,15 @@ class CRM_Core_Payment_Stripe extends CRM_Core_Payment {
     }
   }
 
+  /**
+   * Process incoming notification.
+   */
+
+  static public function handlePaymentNotification() {
+    $data_raw = file_get_contents("php://input");
+    $data = json_decode($data_raw);
+    $ipnClass = new CRM_Core_Payment_StripeIPN($data);
+    $ipnClass->main();
+  }
 }
+