Make use of Javascript extensions to improve performance

XWiki 1.6/1.7/1.8 includes a Javascript extension system allowing to improve performance by conditionnally loading JS or CSS. Since 1.8 it also works with external JS or CSS (not only JS and CSS stored in Skin extensions objects)

http://code.xwiki.org/xwiki/bin/view/Plugins/SkinExtensionsPlugin
http://platform.xwiki.org/xwiki/bin/view/DevGuide/SkinExtensionsTutorial

We can make calls to tell when we need such or such JS or CSS and it will be added to the headers.