title: ExtJs - Checkbox selection model, disable checkbox per row
body: <p>I have a grid with a checkbox selection model.</p>
  
  <pre><code>Ext.define('Mb.view.ship.OrdersGrid', {
      extend: 'Ext.grid.Panel',
      selType: 'checkboxmodel',
      selModel: {
          injectCheckbox: 0,
          pruneRemoved: false
      },
      ...
  </code></pre>
  
  <p>There are some rows that shold not be selectable, based on a value in a field.</p>
  
  <p>In a normal column, I can intervene in the display with <code>renderer</code> and hide the cell content with css (<code>metadata.tdCls</code>), but for the auto generated checkbox column, I cannot find a method to disable or hide the checkbox on a row basis.</p>
  
  <p>Does anyone have an idea how to do this ?</p>