Remove listener limit on supervisor's log stream

Each worker adds 6 listeners to the supervisor's LogWriter when their
logs are fed through the supervisor's stdout. When the maximum number
of listeners (default 10) is exceeded warnings are printed to the
console.
Allow worker log timestamps to be disabled

If the app's log output is already timestamped in-app then it is
harmful to prepend and additional timetamp.
Allow supervisor log timestamps to be disabled

If the log output is being piped through a timestamping log forwarder
then it is harmful to double timestamp log lines.

logger(1), a standard CLI wrapper for syslog(3), is an example of a
log forwarder that adds timestamps.