title: How to perform Header sorting in OnDemandGrid?
body: <ol>
  <li><p>How to do sorting in <code>OnDemandGrid</code> with <code>JSONrestStore</code>?</p>
  
  <p>I tried <code>sortable:true</code> like below but it did not work.</p>
  
  <pre><code> {field: "column1",label: "column1",sortable:true},
   {field: "column2",label: "column1",sortable:true}
  </code></pre>
  
  <p>The normal String sorting itself is not working.</p></li>
  <li><p>I also want to customize the sorting for currency fields and Date fields.  </p></li>
  </ol>
  
  <p>Please tell how to do customized sorting in <code>OndemandGrid</code>.</p>