Automatic network building

[MarcelWaldvogel]

Provide an option (on by default, probably limited to a maximum of automatic nodes) to automatically timestamp from newly-joined timestamping servers.

I.e., timestamping servers acting as clients would provide additional information as part of their requests, which would allow the serving timestamper to learn about their peer. In a soft-state manner, this peer would be added to the list of automatically detected timestampers for a period of time (a few intervals).