title: ExtJS 5 groups following order in grid store
body: <p>Good day! I am grouping data in my grid store using Ext.util.Grouper, but groups are sorted in unacceptable (for my task) way. I need to change sorting algorythm. </p>
  
  <p>My model has fields 'id', 'code' and 'tag'. I try to group records by field 'tag' and sort groups by minimal value of 'code' property in current group.</p>
  
  <p>I tried to solve this problem using groupFn &amp; sortFn in Ext.util.Grouper, but it gave no result :(</p>
  
  <p>Does anybody know, how can this problem be solved?</p>