title: two column with same grouping priority in ui-grid
body: <p>maybe the title of my question is not proper, please feel free to update my title.</p>
  
  <p>my json data is like</p>
  
  <pre><code>    [
          { "AutoId": 2, "CustomerId": "1000AIRLIESST", "customerLastName": "John", "locationId": "2", "Address": "1000   AIRLIES ST Winnipeg " },
          { "AutoId": 2, "CustomerId": "1000AIRLIESST", "customerLastName": "John", "locationId": "186471", "Address": "1000 Airlies ST Winnipeg " },
          { "AutoId": 2, "CustomerId": "1000AIRLIESST", "customerLastName": "John", "locationId": "186752", "Address": "111   pineview rd ST Winnipeg " }
      ];
  </code></pre>
  
  <p>as you can see the autoId, customerId and lastname are same. I want to demonstrate this data in ui-grid like following picture. I want to common part of my data comes in main columns.</p>
  
  <p><a href="https://i.stack.imgur.com/qCKFg.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/qCKFg.png" alt="enter image description here"></a></p>