Rather than initializing the "Dormant" status to "off" and the "last
activity" count to "now", initialize them based on our state file:
stay dormant if we were dormant, or remember the amount of time
we've spent inactive.
Since this is completely core functionality, I'm putting it in
core/mainloop, even though it depends on feature/hibernate. We'll
have to sort that out in the future.
Nick Mathewson