title: Issue silent notifications in android
body: <p>I've read about the notification documentation and audiomanager. I've come across <code>adjustStreamVolume</code> method and <code>STREAM_NOTIFICATION</code> flag. What I'm not understanding at all is how exactly should I apply both this methods if I want to notify the user in silence? Supposing I have the following notification:</p>
  
  <pre><code>notification = new NotificationCompat.Builder(getApplicationContext())
           .setContentTitle(notification_title)
           .setContentText(notification_text)
           .setTicker("Notification!")
           .setWhen(System.currentTimeMillis())
           .setDefaults(Notification.DEFAULT_SOUND).setAutoCancel(true)
           .setSmallIcon(R.drawable.ic_stat_name).build();
  
  //and show with notification manager
  </code></pre>
  
  <p>where exactly does adjustStreamVolume and STREAM_NOTIFICATION fit in all of these?</p>