[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.
Document: cubicweb-doc
Title: CubicWeb Documentation
Author: Logilab
Abstract: Some base documentation for CubicWeb users and developpers
Section: Apps/Programming
Format: HTML
Index: /usr/share/doc/python-cubicweb-documentation/html/index.html
Files: /usr/share/doc/python-cubicweb-documentation/html/*