FairMQ: Extend Multipart and messaging API

- Extend the multipart API to allow sending vectors of messages or helper
   thin wrapper FairMQParts. See example in examples/MQ/8-multipart.
 - NewMessage() can be used in devices instead of
   fTransportFactory->CreateMessage().
   Possible arguments remain unchanged (no args, size or data+size).
 - Send()/Receive() methods can be used in devices instead of
   fChannels.at("chan").at(i).Send()/Receive():
   Send(msg, "chan", i = 0), Receive(msg, "chan", i = 0).
 - Use the new methods in MQ examples and tests.
 - No breaking changes, but FAIRMQ_INTERFACE_VERSION is incremented to 3
   to allow to check for new methods.

fairmq/FairMQDevice.cxx

@@ -666,12 +666,6 @@ void FairMQDevice::InteractiveStateLoop()
     tcsetattr(STDIN_FILENO, TCSANOW, &t); // apply the new settings
 }
 
-inline void FairMQDevice::PrintInteractiveStateLoopHelp()
-{
-    LOG(INFO) << "Use keys to control the state machine:";
-    LOG(INFO) << "[h] help, [p] pause, [r] run, [s] stop, [t] reset task, [d] reset device, [q] end, [j] init task, [i] init device";
-}
-
 void FairMQDevice::Unblock()
 {
     FairMQMessage* cmd = fTransportFactory->CreateMessage();