title: Extjs checkcolumn disable for some rows, based on value
body: <p>I have a grid, with checkcolumn. It's dataIndex is, for example, 'checked'.</p>
  
  <p>I want to disable or hide checkboxes for some rows, where another value, 'can_be_checked' for example, is false/empty.</p>
  
  <p>Renderer is already defined in checkcolumn, messing with it breaks generation of checkbox.</p>
  
  <p>How can I do it?</p>