[etwist] Generates apache's mod_concat-like urls for js and css
Uses the lists of js, css and ie_css included in order to generate
urls compatible with Apache mod_concat (ie: http://test.fr/??file1.js,file2.js).
Css files may use `media` option or may be for IE only ; this patch
does not concatenate css filenames for different media types or
different IE specs.
It concatenates only files served under cubicweb's `data` urls
and keeps original include order.
The generated urls are added to the HTML header as usual.
HOW-TO:
- calling HTMLHead(datadir_url) will enable the url concatenation
- calling HTMLHead() will not benefit of url concatenation
IMPORTANT NOTE:
- fckeditor can no more be served under `/data/` segment