automatically hide undo notification 3 seconds after it has been shown
A timer is used to automatically hide the notification 3 seconds after it is being shown.
The duration is currently not user configurable.
Test Plan: 3 seconds after it is being shown, the notification is automatically removed
Reviewers: Elisa, ngraham
Reviewed By: ngraham
Subscribers: shubham, pino
Differential Revision: https://phabricator.kde.org/D20670