Replace 0MQ with Netty

This is required in order to release from Apache. Because 0MQ/JZMQ is LGPL-licensed, it can't be included as a dependency in Apache releases.

This patch simply removes JZMQ/0MQ and replaces it with the netty transport implementation.

We can still make the 0MQ transport available to users who want to use it. But it will have to be a separate project that's not part of Apache. I will follow up with creating a repo that has the 0MQ transport code in isolation.