add functions to set a custom queue name

[kobayashi]

This introduces new functions to customize queue name from default "celery" to own queue name for each redis and AMQP.
Related Issues: #43 , #136

[grutz]

I really love this change since most celery environments I've worked in have had 4 or more queues to spread out the demand/load. However having to put the queue name in the broker configuration would mean making n+1 brokers for the number of queues.

In python you can pass the queue name across the task request:

https://docs.celeryproject.org/en/stable/userguide/routing.html#manual-routing

from feeds.tasks import import_feed
import_feed.apply_async(args=['http://cnn.com/rss'],
                        queue='feed_tasks',
                        routing_key='feed.import')

This PR is certainly a necessary feature. Passing the queue in the Delay call seems a must as well.

[yoonsio]

@kobayashi @grutz thank you for your pr and feedback.
I prefer to avoid adding any more constructors. We should really look into passing flexible options.
The internal broker queue is exposed as public variable so this feature is already supported.
For example, you can do the following instead of using the constructor.

broker := AMQPCeleryBroker{
  Connection: conn,
  Channel:    channel,
  Exchange:   NewAMQPExchange("myexchange"),
  Queue:      NewAMQPQueue("myqueue"),
  Rate:       4,
}

Please refer to #144