[notification] use new style operation for notification
This results in far less operations created. Operation creation is expensive.
We keep some compatibility with the previous API because some cubes have been
reported to use it.
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/cubicweb-documentation/index.html
Files: /usr/share/doc/cubicweb-documentation/*.html