title: React-native android back button in react-navigation
body: <p>Well, I have a <code>react-native</code> app with multiple screen, each screen having a top bar where a back button is situated, it's main behavior is that the app returns to the main screen when this button is pressed. What I want to do is to copy this behavior to the hardware back button (now by pressing on hardware back button the app closes), how can I do this?</p>
  
  <p><strong>UPDATE:</strong></p>
  
  <p>I'm using <code>react-navigation</code> and <code>redux</code></p>