Add a IPC message queue PubSubAdmin and maybe discovery

[rlenferink]

For local communication and testing purposes it would be nice to have a PubSubAdmin based on the POSIX IPC message queues system. If feasible discovery based on POSIC IPC messages queues would also be nice, but a fallback to use shared memory is maybe more logical for discovery (see also the shared memory based remote service discovery)

A primary goal should be that this PubSub setup should work out of the box with no configuration (as long as the processes are on the same host)

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Original creation date: 31/Jan/2018
Reporter: @pnoltes