title: knockout.js/devExtreme unable to process css-binding
body: <p>I have a dxTileView template which is databound to data coming in from the server. Then, in the template I want to add a css binding which adds a class when the tile is clicked like so...</p>
  
  <pre><code>&lt;div data-bind="dxTileView: {itemClickAction:assignProject, dataSource:quickBooking}"&gt;
            &lt;div data-options="dxTemplate : { name:'item' }" data-bind="css: {selectedTile: selectedTile}"&gt;
              &lt;h4 data-bind="text: blah"&gt;&lt;/h4&gt;
              &lt;p data-bind="text: blah"&gt;&lt;/p&gt;
            &lt;/div&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>And then in the viewmodel I have:</p>
  
  <pre><code>var viewModel = {
          selectedTile: ko.observable(false),
          blah: blah}
  </code></pre>
  
  <p>And the error message:</p>
  
  <pre><code>Uncaught ReferenceError: Unable to process binding "css: function (){return {selectedTile:selectedTile} }"
  Message: selectedTile is not defined 
  </code></pre>
  
  <p>I have tried a few variations on my bindings as follows but none work:</p>
  
  <pre><code>data-bind="css: {selectedTile: viewModel.selectedTile}"//error: viewModel not defined
  data-bind="css: {selectedTile: viewModel.selectedTile()}"
  data-bind="css: {selectedTile: true}" //this works,was just for testing
  data-bind="css: {selectedTile: selectedTile(false)}"//etc etc etc
  </code></pre>
  
  <p>Many thanks in advance for any help!</p>