title: GWT adding widget to Column Header
body: <p>I want to customize my cell table's column header. I have to include support for sorting and filtering. I want to have images for both actions. When the user clicks on the sort image, it will toggle (based on ascending / descending order sort ) and the table sorts based on the icon clicked. I am currenty doing this with some messy HTML manipulation , in the onBrowserEvent of my custom header cell. Could someone tell me how I could use GWT's ToggleButton here?</p>
  
  <p>Thanks.</p>