add isTransparentRedirect function

transparent redirects involve POSTing a form directly to the credit card processor containing the credit card fields
adding this fn to the AbstractResponse means that gateways can be tested to see if they follow that pattern

Author: eileenmcnaughton

src/Omnipay/Common/Message/AbstractResponse.php

@@ -30,6 +30,11 @@ public function isRedirect()
         return false;
     }
 
+    public function isTransparentRedirect()
+    {
+      return false;
+    }
+
     public function getData()
     {
         return $this->data;