title: ExtJS - Combobox with store add a custom selection
body: <p>Is there a way to add without changing an EXT store (myStore.carTypes in this example) an option which just says "None"? with a custom value of ""</p>
  
  <pre><code>type: 'combo',
  fieldLabel: 'Car',
  name: 'carName',
  otrId: 'carName',
  hidden: false,
  allowBlank: true,
  store: 'myStore.carTypes',
  displayField: 'name',
  valueField: 'name',
  maskRe: /
  </code></pre>