[notification] move notification view in ``sobject.notification`` It has no user outside this module. This enforce serversideness of notification and allow future cleanup. No backward compat is set up to prevent circular import. The class has no other user anyway. (closes 2845144)

remove unused import pyflakes say they are unused. Tests suite confirms.

one more merge

[notification] introduce an official `notify_on_commit` function It provides a proper notification api instead of replacing it by yet another clumsy one. Closes #2837251