title: Setting firebase auth ui as first activity
body: <p>I am using default firebase auth ui for my chat application's login purpose</p>
  <p>But when the app is launched , main activity is shown for 1-2 second and then the login page appears</p>
  <p>I want the login screen to be the first screen if the app is launched for first time and if the user is already signed in then skip this activity</p>
  <p>Should i create a different activity and custom login ui and set it attribute to main and launcher in manifest or is there any other way ?</p>