Client-side compiler Feature

This patch adds possibility to use Client-side compilers:
- [FireLESS](https://addons.mozilla.org/en-US/firefox/addon/fireless/)
- Chrome dev tools

This helped me a lot when I started with Bootstrap to find out where exactly css selectors are present.
At the moment feature has only one option: Enable/ Disable, doesn't have language files included and may require some tweaks.

*Note*
The patch adds javascript compiler script and removes `template.css` (or any associated template file) from `<head />`; template.css has to be added either using `JFactory::getDocument()->addStyleSheet($url);` or `JHtml::_('stylesheet', $url);`.
Theoretically it's possible to parse JResponse output and remove stylesheet, but I left it out at the moment.

**Preview**
![FireLESS example](https://addons.cdn.mozilla.net/img/uploads/previews/full/73/73431.png)