Use data-* for CSS and JS files list

This patch removes CSS and JS file info from ajaxPageState and add them to data-js-files and data-css-files attributes on the <script>, <link> and <style> elements. I was able to remove some PHP black magic around settings thanks to that.

This reduce the size of Drupal.setting quite a bit. Everything works the same as before, the file list are fetched from the attributes and sent in the ajax request as usual.

One painful thing was conditional comments. They need to be processed with regexp since they are not in the DOM and can't be accessed with jQuery selectors. The code isn't the prettiest one but it works for now.

Let's see how much it'll break the testbot.