Configure logging and disable it by default

In a rails app of mine I was seeing abysmal performance (several seconds per page) on a page with several of exhibited objects. I tracked it down to the fact that display_case has extremely verbose logging that occurs on every exhibit.

Judging by https://github.com/staqapp/display-case/commit/384659c66d69953379998a01a975ce77054b042b and https://github.com/jredville/display-case/commit/c628641327e00beba47e8e75d170d31f04abd3ef I'm not the only one to come across this.

So, I cherry-picked @jredville 's configuration approach and additionally disabled logging by default.