title: Action column text issue
body: <p>I have a grid <strong>(ExtJs 6)</strong> which extends from <code>'Ext.grid.Panel'</code></p>
  
  <p>I am having one action column in this grid which is defined as follows-</p>
  
  <pre><code>{
      xtype: 'actioncolumn',
      menuDisabled: true,
      text: 'ActionCol Header',
      sortable: false,
      items: [
         { iconCls: 'somecls', xtype: 'button', handler: 'somehandler' }
      ]
  }
  </code></pre>
  
  <p>Here everything works fine except for the text of column.<br>
  The column header displays as expected i.e. 'ActionCol Header' but the text of this column is displaying as '<em>Actions</em>' in the column list which is used to hide/show columns (on click of column menu)</p>
  
  <p>What I am doing wrong here? I tried to add <code>header: undefined</code> but its not working</p>