title: ag-grid grouping not adding expand/collapse controls
body: <p>I'm trying to show some data that is grouped using ag-grid. The data is being displayed correctly, but it is not grouping the data as it should. I'm using angularJS 1.5.8 and ag-grid 12.0.2. Here is a very simplified version of what I'm trying to do:</p>
  
  <pre><code>function _setGridOptions() {
      var data = [
          {packageID: "one", documentID: "one-one", cost: 1},
          {packageID: "one", documentID: "one-two", cost: 2},
          {packageID: "one", documentID: "one-three", cost: 3},
          {packageID: "two", documentID: "two-one", cost: 4},
          {packageID: "two", documentID: "two-two", cost: 5},
          {packageID: "two", documentID: "two-three", cost: 6}
      ];
      var cols = [
          {
              headerName: "Package ID",
              width: 100,
              field: "packageID",
              rowGroup: true
          },
          {
              headerName: "Document ID",
              width: 100,
              field: "documentID"
          },
          {
              headerName: "Cost",
              width: 100,
              field: "cost"
          }
      ];
      $ctrl.agGridOptions = {
          columnDefs: cols,
          animateRows: true,
          enableRangeSelection: true,
          rowData: data,
          enableSorting: true,
          debug: true,
          enableColResize: true,
          onGridReady: function () {
              $ctrl.agGridOptions.api.sizeColumnsToFit();
          }
      };
      $ctrl.transactionsLoaded = true;
  }
  </code></pre>
  
  <p>And here is what the table looks like:</p>
  
  <p><a href="https://i.stack.imgur.com/vGzpR.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/vGzpR.png" alt="enter image description here"></a></p>
  
  <p>As you can see there is no "Group" column and there is no expand/collapse control by the group row.</p>
  
  <p>Any ideas what I'm doing wrong?</p>