Add Datathread plugin framework

...ds/VisualStudio2013/Plugins/LFP_Viewer/LFP_Viewer.vcxproj

Builds/VisualStudio2013/open-ephys.sln

Source/Processors/DataThreads/DataBuffer.h

Source/Processors/DataThreads/DataThread.cpp

Source/Processors/DataThreads/DataThread.h

Source/Processors/PluginManager/OpenEphysPlugin.h

Source/Processors/PluginManager/PluginManager.cpp

Source/Processors/PluginManager/PluginManager.h

Source/Processors/ProcessorManager/ProcessorManager.cpp

Source/Processors/ProcessorManager/ProcessorManager.h

Source/Processors/SourceNode/SourceNode.cpp

Source/Processors/SourceNode/SourceNode.h

Source/Processors/SpikeSorter/SpikeSorter.cpp

Source/Processors/SpikeSorter/SpikeSorter.h