title: extjs 6 combobox reload displayed value
body: <p>when the store is loaded after setValue() we end up with the valueField being displayed. Once the store is loaded and we click on the dropdown, the correct item is being highlighted; but input field itself is not updated with the displayField value.</p>
  
  <p>how do we refresh the input element of the combobox to reflect the selected item display field?</p>