title: Set backgroundColor and Badge for Tabnavigator in React-Navigation
body: <p>In React-Native with React-Navigation I have a Tabnavigator like so:</p>
  
  <pre><code>const testScreenNavigator = TabNavigator({
      Tab1: { screen: Tab1Screen },
      Tab2: { screen: Tab2Screen },
      Tab3: { screen: Tab3Screen },
  });
  testScreenNavigator.navigationOptions = {
      title: 'MY TITLE',
      header: {
          titleStyle:{
          },
          style:{
  // how to set the options?
          },
      }  
  }
  </code></pre>
  
  <p>Now I want to do 2 things:</p>
  
  <ol>
  <li>Set the backgroundColor: 'red' of the Tabs in Android (not iOS bottom tabs)</li>
  <li>Have a badge next to Tab1: e.g. </li>
  </ol>
  
  <h2>Tab1 (2)  |   Tab2   |    Tab3</h2>
  
  <p>Regards</p>