Log Policy and Cleanups

[TheBlueMatt]

At some point in the near future we should improve our logging by:

(a) define a log level at which peers have some "cost" to write to (ie we're already doing disk IO and a peer cannot fill our disk at this level),
(b) define a log level at which we don't log sensitive data (or maybe never do it at all? I believe we don't log secrets at all today),
(c) audit our existing logs for these (#113/#3492),
(d) add additional logging at/move existing logs to the level in (a)
(e) document (a) and (b).

We've kinda loosely done (a) as "you're safe above debug", and (c) may even be easy given that, but there's probably a few that have slipped through.