[*] FO : Improving CSS CCC

When using an absolute URL for import( or url( in CSS, it was creating bugs, so if the url is already an absolute URL, it won't change.
For exemple in case of fonts : @import url(http://fonts.googleapis.com/...);
Merge branch '1.6' of https://github.com/dreammeup/PrestaShop into dreammeup-1.6
Merge branch '1.6' of ssh://github.com/PrestaShop/PrestaShop into 1.6