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/options/FairMQProgOptions.cxx

@@ -101,7 +101,7 @@ int FairMQProgOptions::ParseAll(const int argc, char** argv, bool allowUnregiste
         {
             LOG(WARN) << p;
         }
-        LOG(WARN) << "No channels will be created (You can still fill these manually).";
+        LOG(WARN) << "No channels will be created (You can create them manually).";
         // return 1;
     }