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/nanomsg/FairMQPollerNN.cxx

@@ -16,6 +16,8 @@
 
 #include "FairMQPollerNN.h"
 
+using namespace std;
+
 FairMQPollerNN::FairMQPollerNN(const vector<FairMQSocket*>& inputs)
     : items()
     , fNumItems()