title: Get ID from GCM message
body: <p>Can I get the ID of a GCM message?</p>
  
  <p>When I send a message to GCM Server, it returns an ID. <br>
  I have a table in my database where I store IDs of sent messages.<br>
  When I get the push notification at the client, is there a way to get this ID?</p>
  
  <p>Thanks.</p>