Summary:
when the device notifier pops up automatically, leave it open
if there is no user activity, if there is any, close after around
3 seconds. Suspend the countdown if the notifier window either has
focus or the mouse cursor is over it, leaving the user the time to
go interact. if it doesn't have focus and the mouse leaves, resume
the countdown
replaces D10591

Test Plan:
tested for a while in a real world usage, it behaves in a fairly natural
way

Reviewers: #plasma, broulik

Reviewed By: #plasma, broulik

Subscribers: ngraham, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D10921