Add TCP Receiver

[jsouter]

Adds in the TCP rx thread required for merlin-detector.

[timcnicholls]

Looks good! A few minor comments. It would be great if there was a dummy decoder plugin and integration test added for TCP receivers too 😉

[jsouter]

Cheers Tim, I'll get to work on those changes

[jsouter]

Looking at this again, have made the minor changes to error messages mentioned above and added in a remove_socket call in the TCPRxThread's cleanup_specific_service. Had some issues with getting the build to work when registering a new Dummy decoder class but now I have a DummyTCPFrameDecoder somewhat resembling the Merlin frame decoder. Will set about working on the actual unit tests soon.

[jsouter]

Okay, I removed the *Lib.cpp files from the glob in the CMakeLists.txt as discussed and removed the namespacing of the registrations. I will note that because of recent changes to master using Lambda functions, we may need to add in a set(CMAKE_CXX_STANDARD 11) call somewhere in the CMake, which is absent from this PR.

[GDYendell]

Thanks @jsouter!