Stop buzzing after a while

Any sound notification should be automatically turned off after about 30 minutes. If you're not awake by then, chances are that you're already awake and away.

This will only be possible for sound notifications because there's no way to know how to reverse any commands which have been launched. One possibility is to add two commands to at least every media player - one for starting and one for stopping. I think it would be overly complicated to have two entries for commands in the alarm settings dialog though.