title: Foreground service start once and display activity on click
body: <p>I have 5 activities in my app. Every activity starts the same foreground service.</p>
  <p>In onStartCommand method of the service foreground notification is created which unfortunately means that every call of startForegroundService() in any activity plays notification sound (even though the service is already running). How can I create the foreground notification only once or at least how not to play notification sound on successive startForegroundService() calls?</p>
  <p>The other related question is: how can I go back to my application when I click the foreground notification? I have 5 activites and I would like to reopen the activity that was the last one the user was interacting with.</p>