title: Flutter Firebase Cloud Messaging Message text and title
body: <p>Using Flutter for the first time and have implemented Firebase Cloud Messaging. I can sent a notification from Notification Composer in the Firebase Console. I can see in the debug-console on Android whilst the app is in foreground that it receives the data I have set in Custom Data.</p>
  
  <pre><code>    _firebaseMessaging.configure(
    onMessage: (Map&lt;String, dynamic&gt; message) {
      print('on message $message');
    },
  </code></pre>
  
  <p>However I am wondering how to get not only the Custom Data but also the Message Text and Message Title.</p>