title: Change angular ui-grid's columns visibility
body: <p>I want to show/hide columns after the grid is rendered. Before i moved to the new ui-grid
  I called to <code>toggleVisible()</code> but now it doesn't seem to work.
  I tried to change the column def visibility(or any other property) like bellow </p>
  
  <pre><code>columnDefs[9].visible = false;
  </code></pre>
  
  <p>When I set the visibility on the column definition(before render) it does work, but after wards i cannot change it.</p>