Tracking of Bridge reachability

Item 5.2 on https://trac.torproject.org/projects/tor/wiki/org/sponsors/SponsorE/PhaseOne says: active scanning from within various countries. Nick points out that we should throw in some decoy addresses too.

Creating this ticket isn't all that necessary, but it's a nice way to let other people know which projects I'm working on (and as a reminder to myself).