title: z-index of navigation bar in react-native
body: <p>I have tinder like cards that can be swiped left and right out of screen, 
  but they render below the navigation bar, is there anyway to re-order the index here? 
  My code is setup quite standard, so by logic the bar would always be on top - i think? cant think of anyway around it</p>
  
  <pre><code>renderScene(route, nav) {
      const {globalNav} = nav.props;
      switch (route.name) {
          case 'settings' :
              return &lt;Settings /&gt;;
  
          case 'feed' :
              return &lt;Feed /&gt;;
  
          case 'matches' :
              return &lt;Matches /&gt;;
      }
  }
  
  render() {
      const {globalNav} = this.props;
      return (
          &lt;Navigator
              renderScene={this.renderScene}
              navigationBar={ &lt;Navigator.NavigationBar routeMapper={NavigationBar} /&gt;}
          /&gt;
      );
  }
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/tVsEX.png" rel="nofollow">see screen shot</a></p>