title: ExtJS 4 CheckboxModel and grid columns defaults
body: <p>I have a grid with <code>selType: 'checkboxmodel'</code> and defaults config for its columns, i.e. <code>hidden: true</code>, thus my checkbox column is hidden aswell. Ofcourse I can move defaults properties to columns items and all work just fine but is there way to setup <code>hidden: false</code> for checkbox column?</p>
  
  <p><a href="https://fiddle.sencha.com/#fiddle/13pf" rel="nofollow">Simple fiddle to illustrate issue</a></p>