title: ExtJS 6 - Date Time Picker's numberfield not editable
body: <p>I have tried to extend existing ExtJS6 date picker for date time picker.
  I used <code>numberfield</code> in the date picker as the selection for time.
  However, the number field is not editable. Not only that, the spinner in <code>numberfield</code> once click the date picker is gone.</p>
  
  <p>Can someone enlighten me where did I got it wrong ?
  Why the <code>numberfield</code> is not editable ?</p>
  
  <p>Code in Fiddle.
  <a href="https://fiddle.sencha.com/#fiddle/tc3" rel="nofollow">https://fiddle.sencha.com/#fiddle/tc3</a></p>