luajit was failing to GC the notification about 5% of the time. This
commit stores all widget notifications in a weak table and don't let
any lambda access the parent object notification object.
Each of those changes reduces the failure rate. There might still be
a couple in there, but the test passed 200x on my laptop with 100%
success rate.
The reason is that if actions are provided by rules, only one instance
exist. It was a mistake to couple actions with their notifications. It
could not work reliably and has to be removed.
The commit also change the notification action storage to be a copy
instead of the original table. This allows to append actions (not part
of this commit) without risking adding them to the wrong notification.
**WARNING** This break an unreleased API by removing the `notification`
property of an action.
Emmanuel Lepage Vallee