Refactor AjaxFormLoop, RemoveRowLink and AddRowLink to make mixin useful for these components

The AjaxFormLoop component stores the links in the intitializer call map. In order to modify them in a mixin in the afterRender phase, a public getter for the JavaScriptSupport interface and the JavaScriptSupportImpl class is required.

I need this feature for the cross-site request forgery protection, where I use a mixin to add a token to the rendered event links.