adjust time span of a pinned notification #114

Can we add a settings item at which the user can control the time span, a notification is pinned?
This is mostly targeting towards the automatic pin of a new notification.
Possible time spans which can be selected should include 'forever', which means, that it doesn't collapse by itself, but only when clicked somewhere else or power off the screen.

Point me at the section in the code where the pinned behaviour is controlled and I can have a look at it myself.