Replace UI/Notification with toast notfications

[BurntimeX]

ref #5739
ref https://www.woltlab.com/community/thread/303066-action-success-message/

[eveneme]

What notifications will be supported by toast notifications? It would be great to also add a notification for a new private message, as I often encounter users on the forum who don't notice the new message icon and don't read the message.

[BurntimeX]

From my point of view, the toast notifications should provide direct feedback for actions triggered by the user in the UI (e.g. when deleting an entry).

For general notifications (e.g. about new private messages), there are already browser- or smartphone-based push notifications.

[eveneme]

For general notifications (e.g. about new private messages), there are already browser- or smartphone-based push notifications.

Sure, as long as someone agrees to receive notifications from the browser; otherwise, they will not receive a notification about a new private message.