title: Angular 2.0, how to detect route change on child component
body: <p>How can I detect a route change on a child component?.
  This is what I have tried, but I only see the app component trace the route change.
  I want to be able to detect when the url change from e.g. #/meta/a/b/c to #/meta/a/b/c/d in the MetaDetailView component.</p>
  
  <pre><code>@RouteConfig([
      { path: '/', name: 'Home', redirectTo: ['Meta']},
      { path: '/meta/...', name: 'Meta', component: MetaMainComponent, useAsDefault: true},
      ...other routes...,
    ])    
  export class AppComponent {
      constructor(private _router: Router) {
          _router.subscribe( (url) =&gt; console.log("app.url = " + url));
      }
  }
  
  @RouteConfig([
      { path: '/*other', name: 'Detail', component: MetaDetailViewComponent, useAsDefault: true},
  ])
  export class MetaMainComponent {
      constructor(private _router: Router) {
          _router.subscribe( (url) =&gt; console.log("metamain.url = " + url));
          console.log("MetaMainComponent")
      }
  }
  
  export class MetaDetailViewComponent {
      constructor(private _router: Router) {
          _router.subscribe( (url) =&gt; console.log("metadetail.url = " + url));
          console.log("MetaDetailViewComponent")
      }
  }
  </code></pre>
  
  <p>Thanks
  Jesper</p>