AG-iRODS message queue

[jcnelson]

Make the AG-iRODS listen to the iRODS message queue, to know when to (re)publish data and metadata.

[iychoi]

I'm working on making a library to get events from iPlant Message Queue (RabbitMQ) to combine it with Syndicate AG. Implementing the library is not challenging but verifying whether the message server at iPlant is working correctly and what kind of messages we can receive are still unknown as the message server is a lab test version. I'll figure it out soon.

[iychoi]

The client code of iPlant DataStore and it's message queue (RabbitMQ) is under following repository. AG just need to use it.
https://github.com/iychoi/ids_client