title: remove folder icon in jstree while using checkbox
body: <p>How does one remove the folder icon in jstree whilst using the checkbox plugin?</p>
  
  <pre><code>$('#div').jstree({
          "ui": {
              "theme_name": "checkbox"
          },
          "theme" : { "icons": false },
          "json_data": {
              "ajax": {
                  "type": "POST",
                  "url": "@Url.Action("Tree")"
              }
          },
          "plugins": ["json_data", "checkbox", "ui", "themes"]
      });
  </code></pre>
  
  <p>This all works fine but it displays the checkbox icon as well as the folder icon.</p>