rename ParticleComposition -> Compound

Examples/scatter2d/BiMaterialCylinders.py

Examples/scatter2d/CoreShellNanoparticles2.py

Examples/scatter2d/HexagonalLatticesWithBasis.py

Examples/scatter2d/Interference2DCenteredSquareLattice.py

Examples/scatter2d/Mesocrystal2.py

GUI/Model/BaseItem/SessionItem.h

GUI/Model/CatSample/ItemWithParticlesCatalog.cpp

GUI/Model/FromCore/GUIExamplesFactory.cpp

GUI/Model/FromCore/ItemizeSample.cpp

GUI/Model/Model/ParameterTreeUtils.cpp

GUI/Model/Sample/CompoundItem.cpp

GUI/Model/Sample/CompoundItem.h

GUI/Model/Sample/ItemWithParticles.h

GUI/Model/Sample/LayerItem.cpp

GUI/Model/Sample/MesocrystalItem.cpp

GUI/Model/Sample/ParticleLayoutItem.cpp

GUI/Model/Sample/SampleValidator.cpp

GUI/Model/ToCore/SampleToCore.cpp

GUI/View/Realspace/Particle3DContainer.h

GUI/View/Realspace/RealSpaceBuilder.cpp