title: How to get modified filter value in ag-grid
body: <p>i just started ag-grid, I have created grid with employeename and employeeno as column fields in grid,in grid employeeno column if filter get modify or selected need to get selected employee from filter.
  as document suggested used <strong>onFilterModified</strong> ,function is calling but i want to get employeeno selected in filter.</p>
  
  <p>my grid option as below---</p>
  
  <pre><code>$scope.gridOptions = {
          angularCompileRows : true,
          angularCompileHeaders : true,
          columnDefs : columnDefs,
          debug : false,
          suppressMenuColumnPanel:true,
          suppressRowClickSelection:true,
          floatingTopRowData : createData(),
          rowData : null,
          rowHeight : 35,
          headerHeight : 35,
          enableFilter : true,
          enableSorting : true,
          enableColResize : true,
          rowSelection: 'multiple',
          onGridReady : function(event) {
              event.api.sizeColumnsToFit();
          },
          onFilterModified : callFilterModified
      };
  
   function callFilterModified(){
        alert("test")
    }
  </code></pre>
  
  <p>please give some suggestion over this.</p>