append javascript after CSS

append javascript after CSS

Javascript resources should be presented to browsers after CSS, and
"after the fold" (ATF) according to the best practices:

https://developers.google.com/speed/docs/insights/mobile#PutStylesBeforeScripts

This change allows the browser to download Javascript files in
parallel, by including Javascript on the *closing* </body> tag instead
of the opening tag.

We also improve the regex to tolerate spaces before the body tag, as
some templates have (proper) indentation for the tag.