log output: add DEBUGV and begin cleanup

* add DEBUGV loglevel
* move most of the huge log outputs to DATADUMP
* move most of the really frequent log outputs to DEBUGV

Next I'm reevaluating the log level assigned to each output and the information they provide. Ideally I'm thinking the default log level should be INFO (20) and should give the user a good picture of what their node is doing on the network without being too much or too many to read in realtime.
This import style is advocated by pylint, too (try enabling `W0403`). Let's give it a shot.