title: access property of controller from within view
body: <p>I wanna do something like a progress bar, which will be controlled by ember. So in my eyes, there are two and a half ways to achieve this:</p>
  
  <ol>
  <li><p>Have an observer in the <strong>controller</strong>, which sets the elements' <code>width</code> when triggered. Problem: AFAIK, one can't access DOM-elements from within the controller, i.e. like the way you'd do it in the view <code>this.$('#progress')</code>. </p></li>
  <li><p>Have an observer in the <strong>view</strong>, which observes the controller's property. Problem: I don't know, how to observe (and access) a controller's property.</p></li>
  <li><p><em>(bind the controller's property via <code>{{bindAttr}}</code> to a freaky <code>data-progress="42"</code> attribute and adjust the elements <code>width</code> whenever the attribute's value has changed)</em></p></li>
  </ol>