Named queues (configurable redis key prefix)

Modified the Redis keys that Kue uses to make the prefix configurable. My two use cases:

* Run functional tests of my application which uses Kue in isolation
* Allow multiple applications that use Kue to use the same Redis instance without polluting each other.

redis.queueName ends up behaving similarly to redis.createClient - override it once for your application and everything should just work.

I built this off the develop branch as I needed some of the functionality that's been cropping up there.

Also, thanks for keeping this moving, behrad!  Good to see changes coming along!