- 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.cxx

@@ -52,8 +52,11 @@ std::ostringstream& FairMQLogger::Log(int type)
         case ERROR:
             type_str = "\033[01;31mERROR\033[0m";
             break;
+        case WARN:
+            type_str = "\033[01;33mWARN\033[0m";
+            break;
         case STATE:
-            type_str = "\033[01;33mSTATE\033[0m";
+            type_str = "\033[01;35mSTATE\033[0m";
         default:
             break;
     }