Bug 483481

Title is somewhat self-explanatory. If an application sends too many notifications in a short interval, Plasma becomes unresponsive as it processes the notification deluge. While undoubtetly an application programming error, Plasma should be robust against this.

A simple while loop in bash can replicate this:
```
while true; do
  echo "^G" # this is BEL and it needs to be inputted as ctrl+v ctrl+g
done
```
and switch to another tab in Konsole. (notify-send will trigger the "too many same notifications" error.)

If you're curious, the application on my system that results in this is sbt.