Make dblogger be yakonfigurable; add --verbose and other flags.

If you yakonfig.parse_args(..., [..., dblogger, ...]), then the default
logging setup shows up in --dump-config output and you get the specified
logging setup before control returns to you.

The default setup is INFO-level logging to stdout.  --verbose makes this
more verbose (e.g., DEBUG-level); --quiet less (WARNING); and
--debug logger enables debug-level output but only for 'logger'.