Add persistent resident notification when timer is running
This allows to control a timer (pause, resume, reset, add a minute) even when KClock isn't running. Particularly when launching a timer through KRUnner there was previously no indication that something was going on.
An option is added to show the notification always, only when KClock isn't running (the default), never.
Needs plasma/plasma-workspace!5359 (merged) for the minimize feature
Needs frameworks/knotifications!172 (merged) for updating the pause/resume button to work