title: Need to add a custom option in Ember Select
body: <p>How can I include a custom option (say, Quick Create) after the prompt in an Ember Select (with optgroups) ?
  For example: I want my  options in ember select to look like this:</p>
  
  <blockquote>
  <pre><code>Select
  Add
  Group1
   Option1
   Option2
  Group2
   Option1
   Option2
  ...
  ...
  </code></pre>
  </blockquote>