I've seen people complaining about ugly notification popups when they were in fact running Dunst instead of Plasma.
Since the KCM won't work with notifications other than Plasma's, this patch adds a hint informing the user when there is no notification widget or notifications are provided by another service than Plasma.
Notification API provides a way to query server identity which is used to determine if it's Plasma or not. The process name isn't used as you could have a notifications widget in e.g. Latte Dock.
Depends on D25772