[DO NOT MERGE] Implement ApplicationMessageListener provided by rabbitmq-consumer

This is not pull request but feature sample.

This listener can get gerrit events using [rabbitmq-consumer] [1]. If there is a tool which store gerrit event to RabbitMQ queue, we would be liberated from ssh stream connection.

But this patch has some issues:

* This can be used when gerrit stream connection is started.
* This patch requires jenkins 1.480.3 or later.

First is GerritHandler related issue. now GerritHandler handles event and connection for gerrit. Even if we want to use gerrit event handling feature only, we have to start connection.

I try to avoid it, but seems heavy implementation. It's quite impossible for me to provide it...

If possible, connection handling should be decoupled from this handler. How do you think?

[1]: https://wiki.jenkins-ci.org/display/JENKINS/RabbitMQ+Consumer+Plugin        "rabbitmq-consumer"