Update multi-part features (nanomsg) and various fixes

- Implement nanomsg multipart with MessagePack.
 - Use the MessagePack from FairSoft and handle not found case.
 - Update splitter, merger and proxy devices to handle multi-part.
 - Let FairMQParts.At() return pointer reference (can be used for moving).
 - Add missing const specifier in the message interface.
 - Add transmit kernel size setting to channels (ZMQ_SNDBUF).
 - Remove FairMQBuffer device.
 - Remove old multi-part methods from Tutorial3 example (to be replaced with Parts API).
 - Make callback mandatory for newMsg(data, size, callback).
 - Add missing <vector> include in FairMQSocket.

examples/MQ/4-copypush/FairMQExample4Sampler.cxx

@@ -34,7 +34,10 @@ void FairMQExample4Sampler::Run()
 
         uint64_t* number = new uint64_t(counter);
 
-        std::unique_ptr<FairMQMessage> msg(NewMessage(number, sizeof(uint64_t)));
+        std::unique_ptr<FairMQMessage> msg(NewMessage(number, // data pointer
+                                                      sizeof(uint64_t), // data size
+                                                      [](void* data, void* hint){ delete static_cast<uint64_t*>(data); } // callback to deallocate after the transfer
+                                                      ));
 
         LOG(INFO) << "Sending \"" << counter << "\"";