title: Ember.js check if value is in array attribute
body: <p>I have a Game model like this:</p>
  
  <pre><code>App.Game = DS.Model.extend({
      numbers: DS.attr(),
      drawnNumbers: DS.attr()
  });
  </code></pre>
  
  <p>The content of <code>numbers</code> is</p>
  
  <pre><code>[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,
              16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,
              31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,
              46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,
              61,62,63,64,65,66,67,68,69,70,71,72,73,74,75]
  </code></pre>
  
  <p>And the <code>drawnNumbers</code> attribute is a empty array (by default)</p>
  
  <p>My view loops over all numbers</p>
  
  <pre><code>{{#each number in numbers}}
      &lt;li data-number="{{number}}" class="number"&gt;&lt;a&gt;{{number}}&lt;/a&gt;&lt;/li&gt;
  {{/each}}
  </code></pre>
  
  <p>When a number exists in the drawnNumbers array I want to add a class <code>active</code>.</p>
  
  <p>How would I go and do this?</p>