[UI-Library] Notifications property has wrong content

[pls78]

In the Settings page, the Notifications component, which is the parent for each Notification displayed, has a notifications prop which is exposed through a notifications HTML attribute of the aside HTML entity (see packages/js/src/settings/components/notifications.js).
This results in notifications=[object object] when a notification is show, which I don't think is the intended behaviour.
We should investigate what the notifications attribute was meant to hold and change the code accordingly.