Make the redis and resque databases configurable

Hello, 

I noticed that Barkeep doesn't play well with other applications that use Resque to perform jobs asynchronously. Workers of those apps show up in Barkeep's resque web interface and vice versa. Jobs being enqueued might end up being processed by those workers, which results in errors.

Therefore, I thought it might be a good idea to make the Redis and Resque database configurable in environment.rb. I added some sane defaults, though.

What do you guys think?