Added general logging settings.

Hi there, I added a basic logging configuration in the `common.py` settings. With this, you can actually have Python tracebacks on the console when developing the suite or in a file if you configure it for that when running in a server. Errors mailing to admins is also available. I missed this logging when trying Gunnery in my local.

You wrote a nice piece of software :) I think I'll give it a try in a couple of projects.

Hope you find this useful!