Fix problems with message saving

Source/Processors/Channel/Channel.cpp

Source/Processors/GenericProcessor/GenericProcessor.cpp

Source/Processors/GenericProcessor/GenericProcessor.h

Source/Processors/LfpDisplayNode/LfpDisplayNode.cpp

Source/Processors/MessageCenter/MessageCenter.cpp

Source/Processors/NetworkEvents/NetworkEvents.cpp

Source/Processors/NetworkEvents/NetworkEvents.h

Source/Processors/PSTH/PeriStimulusTimeHistogramNode.cpp

Source/Processors/RecordNode/HDF5Recording.cpp

Source/Processors/RecordNode/OriginalRecording.cpp

Source/Processors/RecordNode/RecordNode.cpp