Exspose pipeline network and status through zmq

[Nitnelav]

Just an idea, because I like ZeroMQ and because it's allready a dependency :)

We could expose the state of the pipeline through a zmq api. The network structure could be exposed with a REQ-RES pattern and the various nodes' states through a PUB-SUB pattern.
The REQ-RES pattern could also be used for "control" requests like : run X, invalid cache for X, pause after X, etc...
That would enable any HMI technology to be used on top of it...

[sebhoerl]

Yes, I think it is a good idea :)