[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

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<div id="ajaxroot">

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  <div class="ajaxHtmlHead">

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    <script src="http://foo.js" type="text/javascript"> </script>

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  </div>

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  <h1>Hello</h1>

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</div>