title: widgetcolumn: bind visibility of widget to dataIndex
body: <p>I have a widgetcolumn that contains a button:</p>
  
  <pre><code>xtype:'widgetcolumn',
  dataIndex: 'canUpdateKey',
  itemId:'updateKey',
  width:120,
  widget: {
      xtype: 'button',
      text: 'Update key',
      hidden: '{!record.canUpdateKey}'
  }
  </code></pre>
  
  <p>I only want to display the button where <code>canUpdateKey</code> is true on the record; but this does not work as indented. <a href="https://fiddle.sencha.com/#view/editor&amp;fiddle/26ie" rel="nofollow noreferrer">Relevant fiddle</a></p>