title: ng-options with disabled rows
body: <p>Is it possible to use <code>ng-options</code> that it will render into disabled rows based on criteria? </p>
  
  <p>this:</p>
  
  <pre><code> &lt;select ng-options="c.name group by c.shade for c in colors"&gt;
  </code></pre>
  
  <p>maybe possible to turn into something like this:</p>
  
  <pre><code> &lt;select ng-options="c.name group by c.shade for c in colors | disabled(c.shade)"&gt;
  </code></pre>
  
  <p>and let's say via a filter that could return <code>disabled='disabled'</code> for all the colors that have shade = "dark"</p>
  
  <pre><code>&lt;select&gt;
     &lt;optgroup label="dark"&gt;
        &lt;option value="0" disabled="disabled"&gt;black&lt;/option&gt;
        &lt;option value="2" disabled="disabled"&gt;red&lt;/option&gt;
        &lt;option value="3" disabled="disabled"&gt;blue&lt;/option&gt;
     &lt;/optgroup&gt;
     &lt;optgroup label="light"&gt;
        &lt;option value="1"&gt;white&lt;/option&gt;
        &lt;option value="4"&gt;yellow&lt;/option&gt;
     &lt;/optgroup&gt;
   &lt;/select&gt;
  </code></pre>