[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.
missing-dep-for-interpreter make => make | build-essential | dpkg-dev (usr/*/cubicweb/skeleton/debian/rules)
embedded-javascript-library usr/share/cubicweb/cubes/shared/data/jquery.js