title: ng-grid Event for Selection checkbox on header
body: <p>I am using ng-grid of AngularUI-Grid, and having a checkbox for row selection. It gives me a checkbox in header too. </p>
  
  <p>If user selects checkbox in header, I want some event/method to trigger in $scope, is there any way? I thought by specifying :- checkboxHeaderTemplate , I would get toggleSelectAll() method would get called. but it is not happening. Any clue?
  Also is there any Event or method of $scope which can get called on multiple row selection or un-selection.</p>
  
  <pre><code> $scope.gridOptions = {
                data: 'dataList',
                enablePaging: true,
                showFooter: true,
                showFilter: true,
                totalServerItems: 'totalVehicles',
                pagingOptions: $scope.VehpagingOptions,
                filterOptions: $scope.VehfilterOptions.filterText,
                showSelectionCheckbox: true,
                beforeSelectionChange: $scope.beforeVehicleSelectionChange,
                checkboxHeaderTemplate: '&lt;input class="ngSelectionHeader" type="checkbox" ng-show="multiSelect" ng-model="allSelected" ng-change="toggleSelectAll(allSelected, true)"/&gt;'
            };
  </code></pre>