title: Angularjs ag-grid header cell click event is not firing up
body: <p>In ag-grid, one of the header columns I have the following :</p>
  
  <pre><code> headerCellRenderer : function(params) {
                          params.$scope.assignRegHrsInput = "";
                          return '&lt;span&gt;' + data.headerName + '&lt;/span&gt;&lt;/br&gt;&lt;input class="exp-param-header-input"  type="text" ng-model="assignRegHrsInput"&gt; &lt;/br&gt; &lt;span ng-click="changeAllAssignedRegHrs(assignRegHrsInput)"&gt; &lt;span class="glyphicon glyphicon-download"&gt;&lt;/span&gt; Apply To All&lt;/span&gt;'
                      }
  </code></pre>
  
  <p>And I have </p>
  
  <pre><code> $scope.changeAllAssignedRegHrs = function(tobeChanged) {
     alert(tobeChanged);
   }
  </code></pre>
  
  <p>But the when I click the above span element click event is not firing up. Can any help me how to fix it?</p>
  
  <p>In my grid options I have specified :</p>
  
  <pre><code>angularCompileRows: true,
  angularCompileHeaders: true
  </code></pre>
  
  <p>But still the ng-click event on the span is not firing up.</p>
  
  <p>In the browser console, I can see my header for this span as shown below:</p>
  
  <pre><code>&lt;span class="ng-scope"&gt;
  &lt;span&gt;R Hours&lt;/span&gt;
  &lt;br&gt;
  &lt;input class="exp-param-header-input ng-pristine ng-untouched ng-valid" type="text" ng-model="assignRegHrsInput"&gt;
  &lt;br&gt;
  &lt;span ng-click="changeAllAssignedRegHrs(assignRegHrsInput)"&gt;
  &lt;span class="glyphicon glyphicon-download"&gt;&lt;/span&gt;
  Apply To All
  &lt;/span&gt;
  &lt;/span&gt;
  </code></pre>