title: react-native-navigation : How to hide header to all the screens
body: <p>I am able to <code>hide header</code> in my <code>stackNavigator</code> like this:</p>
  
  <pre><code>const StackNavigator = createStackNavigator({
    ScreenOne:{
    screen:ScreenOne,
    navigationOptions: {
      header: null
      }
    }
  })
  </code></pre>
  
  <p>But if I have multiple screens, and want to apply <code>header:null</code> to all the screens, how can I set the <code>navigationOptions</code>? 
  For example, I tried this but won't work.</p>
  
  <pre><code>const StackNavigator = createStackNavigator({
      ScreenOne:ScreenOne,
      ScreenTwo:ScreenTwo,
      ScreenThree:ScreenThree,
      navigationOptions: {
          header: null
    }
  })
  </code></pre>