Limit log size and/or duration

[daveschaefer]

We don't want notary logs to get out of hand. Let's add a log handler to delete logs older than 30 days or a certain filesize so they don't consume an entire disk.

This is built in to python - http://docs.python.org/2/library/logging.handlers.html#rotatingfilehandler

In the spirit of using default values to make it easy for anyone to quickly run a notary, let's default to 30 days and let people specify a different value if they wish.

[daveschaefer]

In v3.4 there is a --quiet argument if you wish to suppress most log data, but that is a different aim than this ticket.