[entities] Introduce an IDublinCore adapter
Move all dc_ methods from AnyEntity to the new IDublinCore adapter and proxy
them through a __getattr__ method on AnyEntity.
Current test suite should be enough.
Closes #3119992.
version=3
opts=uversionmangle=s/(rc|a|b|c)/~$1/ \
https://pypi.debian.net/cubicweb/cubicweb-(.+)\.(?:zip|tgz|tbz|txz|(?:tar\.(?:gz|bz2|xz)))