Add global samplerate to help timestamping events

Source/CoreServices.cpp

Source/CoreServices.h

...Plugins/BasicSpikeDisplay/SpikeDetector/SpikeDetector.cpp

Source/Plugins/LfpDisplayNode/LfpDisplayNode.cpp

Source/Plugins/PhaseDetector/PhaseDetector.cpp

Source/Plugins/PhaseDetector/PhaseDetector.h

Source/Plugins/SerialInput/SerialInput.cpp

Source/Processors/AudioNode/AudioNode.cpp

Source/Processors/Channel/InfoObjects.cpp

Source/Processors/Channel/InfoObjects.h

Source/Processors/Channel/MetaData.cpp

Source/Processors/Channel/MetaData.h

Source/Processors/GenericProcessor/GenericProcessor.cpp

Source/Processors/GenericProcessor/GenericProcessor.h

Source/Processors/MessageCenter/MessageCenter.cpp

Source/Processors/MessageCenter/MessageCenter.h

Source/Processors/MessageCenter/MessageCenterEditor.cpp

Source/Processors/MessageCenter/MessageCenterEditor.h

Source/Processors/ProcessorGraph/ProcessorGraph.cpp

Source/Processors/SourceNode/SourceNode.cpp