title: kendo Datasource return custom value
body: <p>I have a remote datasource like this, </p>
  
  <pre><code>var datasource = new kendo.data.DataSource({
      autoSync: false,
      batch: true,
      transport: {
          read: {
              url: "some_url",
              dataType: "json"
          }
      },
      serverFiltering: true,
      serverGrouping: true,
      serverPaging: false,
      page: 1,
      pageSize: 10,
      schema: {
          data: "results",
          total: "total",
          model: {
              id: "id"
          }
      }    
  });
  </code></pre>
  
  <p>And I would like to get one additional value from the serverside like this. </p>
  
  <pre><code>    $response = array(
          'results' =&gt; $product_alerts,
          'total'   =&gt; $total,
          'total_approved_products'  =&gt; 27
      );
      echo json_encode($response);
      exit;   
  </code></pre>
  
  <p>Is there anyway I can get the value of total_approved_products in ClientSide ? </p>
  
  <p>Many thanks</p>