title: Sort Grouped Columns in AdvancedDatagrid
body: <p>I#m looking for a solution to sort all grouped colums in advancedDatagrid. It should be the same behavior like clicking in a columns head.</p>
  <p>Please note, i'm not looking for a solution to sort the fields IN a the grouping. There is working solution named compareFunction.</p>
  <p>But I'm not able to sort the two rows in my picture by column &quot;Einnahmen&quot;. Sorry for the german word.
  Do you have an Idea?
  <img src="https://i.stack.imgur.com/j9vmQ.jpg" alt="enter image description here" /></p>
  <p>Thank you
  Frank</p>