title: subscribe to ionic page change event
body: <p>In angular2 we can subscribe to Router events as shown below:</p>
  
  <pre><code>router.events.subscribe((event: RouterEvent) =&gt; { /* detects route/navigation change*/
   //some logic to show loading image
  });
  </code></pre>
  
  <p>How do I translate above code for use in Ionic 2?</p>