title: keypress to delete value in 'open' datefield and close related datepicker
body: <p>I have an ExtJS form.field.Date as below;</p>
  
  <pre><code>{
      xtype: 'datefield',
      name: 'X_Cut_Process_Completed_Date',
      format: 'd M Y',
      startDay: 1,
      allowBlank: true,
      editable: false,
      listeners: {
          specialkey: function(field, e){
              if (e.getKey() == e.DELETE) {
                  field.setValue('');
              }
          }
      }
  }
  </code></pre>
  
  <p>I have been asked to implement an event that catches the Delete key while the <code>datefield</code> is being edited (with the associated <code>datepicker</code> open), that clears the value for the <code>datefield</code> and closes the <code>datepicker</code>. The existing <code>specialkey</code> listener only clears the value while the <code>datefield</code> is NOT being edited.</p>
  
  <p><strong>How do I implement a listener that closes a <code>datefield</code>'s <code>datepicker</code> and clear the <code>datefield</code>'s value simultaneously?</strong></p>