Deactivate Caffeine after a certain period of user inactivity

This would effectively prolong the screensaver or logout timeout on machines where group policies enforces some fixed, often too short interval. My machine is fixed to 5 minutes, so setting the Caffeine interval to 25 minutes would give me a 30 minute interval in total.
Of course Caffeine should re-activate again after wakeup.

In order to get notified about user activity, Caffeine would need to register for all keypresses.  There's a lot of security software which takes a dim view of this.  It might be legit in this case, but many executable which ask for a preview of all keypresses are likely to be malicious.  That's why I plan to steer clear of that function, sorry.

Tom