Added couple optional parameters to RabbitMQConnection for:

* Alternative list of addresses when RMQ works in HA mode
* Custom ExecutionService for consumer threads

Actually I added couple parameters from this part of the [RabbitMQ API](http://www.rabbitmq.com/api-guide.html#advanced-connection). If this change can be integrated with 1.3 - that would be great, I tried but did not find where the version is stored.

Thanks