Dependency Isolation

[jmwample]

Now that we are tracking both client and station code in a mono-repo we need to slice things into more than one module and be careful to not require station dependencies (like libzmq) when building the client.

[mingyech]

For the issue of the transports importing from pkg/station/lib therefore importing zmq in the client, I've made the transports use an interface for the dependencies so that they do not import them. In the station application, we can use dependency injection to pass the required dependencies to the transports.