[web/data] Fix userCallbackThenUpdateUI to completely replace old DOM elements Without the 'swap' parameter, userCallbackThenUpdateUI() would replace the _children_ of the component with a new version of the componenent, thus creating nested divs/spans/buttons/etc. Closes #4881299

<div id="ajaxroot">
  <div class="ajaxHtmlHead">
    <script src="http://foo.js" type="text/javascript"> </script>
    <link rel="stylesheet" type="text/css" media="all" href="qunit.css" />
  </div>
  <h1>Hello</h1>
</div>