add addStack

Sample/Multilayer/LayerStack.cpp

Sample/Multilayer/LayerStack.h

Sample/Multilayer/Sample.cpp

Sample/Multilayer/Sample.h

auto/Examples/scatter2d/CorrelatedRoughness.py

auto/Examples/specular/RoughnessModel.py

auto/FigExamples/scatter2d/CorrelatedRoughness.py

auto/FigExamples/specular/RoughnessModel.py

auto/MiniExamples/scatter2d/CorrelatedRoughness.py

auto/MiniExamples/specular/RoughnessModel.py

auto/Wrap/libBornAgainSample.py

auto/Wrap/libBornAgainSample_wrap.cpp

rawEx/scatter2d/CorrelatedRoughness.py

rawEx/specular/RoughnessModel.py