merge remaining pixel classes

Base/Pixel/IPixel.h

Base/Pixel/Pixel.cpp

Base/Pixel/Pixel.h

Device/Detector/Detector2D.cpp

Device/Detector/Detector2D.h

Device/Detector/IDetector.h

Device/Detector/OffspecDetector.cpp

Device/Detector/OffspecDetector.h

Device/Detector/SphericalDetector.cpp

Device/Detector/SphericalDetector.h

Resample/Element/DiffuseElement.cpp

Resample/Element/DiffuseElement.h

Sim/Simulation/OffspecSimulation.cpp

Sim/Simulation/OffspecSimulation.h

Sim/Simulation/ScatteringSimulation.cpp

Sim/Simulation/ScatteringSimulation.h

auto/Wrap/libBornAgainDevice.py

auto/Wrap/libBornAgainDevice_wrap.cpp