title: Send notification once in a week
body: <p>I want to notify the user about answer the weekly questions.I need to send the notification to the user even my app is not running.The notification will send once in a week. 
  When user clicks the notification my app will gets open.
  I tried this via Timer and TimerTask().This notifies the user when my app is running.How can I send the notification to the user while app is not running.</p>
  
  <p>Anyone can help me out?</p>