[web] Add datadir-url configuration option (closes #5204550) Makes it possible to use a different host for static data instead of ${base_url}/data

version=3
opts=uversionmangle=s/(rc|a|b|c)/~$1/ \
http://pypi.debian.net/cubicweb/cubicweb-(.+)\.(?:zip|tgz|tbz|txz|(?:tar\.(?:gz|bz2|xz)))