- Add multipart support to the interface and enable its use out of tasks.

Examples on the use out of tasks are provided in:
  `example/Tutorial3/digitization/TestDetectorDigiLoader.tpl:76-85`: sending a part.
  `example/Tutorial3/reconstruction/FairTestDetectorMQRecoTask.tpl:177-182`: receiving a part.

- This commit also makes structure within processorTask more consistent with samplerTask.

- add macro MQLOG to FairMQLogger.

fairmq/FairMQLogger.h

@@ -31,6 +31,7 @@ class FairMQLogger
         DEBUG,
         INFO,
         ERROR,
+        WARN,
         STATE
     };
     FairMQLogger();
@@ -46,5 +47,6 @@ typedef unsigned long long timestamp_t;
 timestamp_t get_timestamp();
 
 #define LOG(type) FairMQLogger().Log(FairMQLogger::type)
+#define MQLOG(type) FairMQLogger().Log(FairMQLogger::type)
 
 #endif /* FAIRMQLOGGER_H_ */