Add support for ZMQ PubSub model

[deepbrook]

As it stands now, the client is at risk to eventually crash due to an MemoryError, if the user doesn't clear the Queues fast enough.

Using ZMQ to provide data moves this risk to the subscriber, instead of the client (which then would become the publisher). This is, IMO, more favorable, since Slow-Subscriber-Syndrome can be fought using the Suicidal-Snail-Pattern. Either way, the Client would run smoother and be rid of a weakspot in its architecture.

Since ZMQ requires substantially different architecture to implement, we should add the ZMQ-enabled client as a separate class, letting the user choose for themselves.