[cwproperties] refactor properties form to make it partly overrideable easily (closes #1936782) also fix some pitfalls on the way: * shouldn't capitalize labels, this has to be done in translation files as desired * form_row in CWProperties form didn't return subform as its parent class

<div id="ajaxroot">
  <div class="ajaxHtmlHead">
    <script src="http://foo.js" type="text/javascript"> </script>
  </div>
  <h1>Hello</h1>
</div>