Demos: fixed inactive Loader demo

JavaScript for Loader options demo was under the `<head>` tag, which prevented it from activating when the page was AJAX-loaded. Relevant script tag has been moved to the `data-role="page"` element.

See working version from 1.2 docs [here](https://github.com/jquery/jquery-mobile/blob/1.2-stable/docs/config/loadingMessageTextVisible.html).