Notification: Implement timing functions on Container (and remove timing functions from toast)

[iszmais]

THIS PR DEPENDS ON https://github.com/ILIAS-eLearning/ILIAS/pull/7654

https://mantis.ilias.de/view.php?id=41514

In general, this clears up the timing responsibility of toast by appending it to the container. Further, this removes trivial artifacts from the toast themself.