Replace NULL by nullptr.

Core/DataStructures.hpp

Core/Factory.hpp

Core/Simulator.cpp

Core/UnitTests/Factory.cpp

Core/ViewerBase.cpp

Core/WorkerThread.h

Devices/NIDAQmx.h

Devices/NIUSB6008Interface.cpp

Examples/AlphaMap/AlphaMappingExample.cpp

Mesh/Mesh.cpp

Mesh/Mesh.h

Mesh/SurfaceMesh.cpp

Mesh/VegaSceneObject.cpp

Mesh/VegaSceneObject.h

Rendering/FrameBuffer.cpp

Rendering/GLUtils.cpp

Rendering/GLUtils.h

Rendering/MetalShader.cpp

Rendering/Shader.cpp

Rendering/VAO.cpp