Enable new callback API

- OnData() channel data handler.
 - ConditionalRun() for devices without incoming data.
 - Header file with common main(), to be extended with getDevice/addCustomOptions.
 - Update examples (MQ/Tutorial3) to use the new API and config.
 - NewSimpleMessage() for simpler creation of small messages (additional copy).
 - Replace SetProperty/GetProperty with fConfig access.
 - Runtime configurable channel names for common devices.
 - Configurable logging interval per channel.
 - FairMQMultiplier for distributing same data to multiple outputs.
 - Cleanup state machine messages.
 - Cmd option to toggle signal handling.
 - Simpler API for send/receive timeouts.
 - Enable --log-to-file.
 - Fix coverity issues, warnings.
 - Various code cleanup and minor tweaks.

examples/MQ/1-sampler-sink/FairMQExample1Sink.cxx

@@ -19,21 +19,17 @@ using namespace std;
 
 FairMQExample1Sink::FairMQExample1Sink()
 {
+    // register a handler for data arriving on "data" channel
+    OnData("data", &FairMQExample1Sink::HandleData);
 }
 
-void FairMQExample1Sink::Run()
+// handler is called whenever a message arrives on "data", with a reference to the message and a sub-channel index (here 0)
+bool FairMQExample1Sink::HandleData(FairMQMessagePtr& msg, int /*index*/)
 {
-    while (CheckCurrentState(RUNNING))
-    {
-        unique_ptr<FairMQMessage> msg(NewMessage());
+    LOG(INFO) << "Received: \"" << string(static_cast<char*>(msg->GetData()), msg->GetSize()) << "\"";
 
-        if (Receive(msg, "data") >= 0)
-        {
-            LOG(INFO) << "Received message: \""
-                      << string(static_cast<char*>(msg->GetData()), msg->GetSize())
-                      << "\"";
-        }
-    }
+    // return true if want to be called again (otherwise go to IDLE state)
+    return true;
 }
 
 FairMQExample1Sink::~FairMQExample1Sink()