Better logging support

[magnusbaeck]

Description

When the code has something to say it should use the standard logging module instead of today's print statements (used in just a couple of places). When running the web app we can configure the logging via Gunicorn, but when running storage.py standalone we should accept a --logconfig argument (or similar) that loads logging configuration with dictConfig() like gunicorn can do.

Motivation

That's the standard way of logging messages and will allow users to get timestamps, custom output formats, and what-not.

Benefits

I'd expect anyone deploying this to production to want to have proper logs. Externalizing the logging configuration will also make it possible to adjust the level of loggers deeper down in the stack, e.g. pika.

Possible Drawbacks

None.