[Html-widget] javascript support fixed

[Carl Franks]

JS support was broken, as the  <!-- --> comment tags and other
characters were being wrongly html-encoded, causing the browser to not
execute the JS (tested with FF).

It's now fixed so the contents of $container->javascript() are not encoded.

At the same time I've taken the liberty to change $result->as_xml(),
so that the javascript is printed after the element, rather than
before.
I've confirmed that HTML-Widget-JavaScript's tests still pass, and I
don't think it'll affect anyone else, as the JS output was broken
anyway.

Carl