Rename device property to have a common format and some code cleanup.

FairMQDevice: Rename property for socket rate logging to have common format (old name is still available for compatibility).
FairMQ: Avoid using std namespace in class headers (may require adding std namespace to some child devices).
FairMQ: A bit of code cleanup
FairMQConfigurable: Stop with an error if a property assignment failed due to incorrect key.

fairmq/prototest/FairMQProtoSampler.cxx

@@ -22,6 +22,8 @@
 
 #include "payload.pb.h"
 
+using namespace std;
+
 FairMQProtoSampler::FairMQProtoSampler()
     : fEventSize(10000)
     , fEventRate(1)