Display the full Redis connection in Web footer

The web interface shows the Redis location in the footer.

Since we can connect to Redis with the full array of options, we can have a combination of socket and non-0 database, which would not be properly displayed.

The Redis client supports an `#id` method that just does what we need.

I've added a helper method `#redis_connection` that delegates to Redis' client ID method.

![sidekiq 2013-10-22 16-23-09](https://f.cloud.github.com/assets/5142/1381777/7ada7c98-3b25-11e3-87d4-8a1186638a4e.png)

Since there is no test for this, I've not added some, and I didn't delete the existing `#location` helper either.