the nuclear stack extension with unit test and all needed adaptions

Documentation/Examples/stack_example.cc

Environment/Environment.h

Environment/FlatAtmosphere/FlatAtmosphere.h

Environment/HomogeneousMedium.h

Environment/IMediumModel.h

Environment/NuclearComposition.h

Environment/VolumeTreeNode.h

Environment/testEnvironment.cc

Framework/Cascade/Cascade.h

Framework/Cascade/Step.cc

Framework/Cascade/testCascade.cc

Framework/Geometry/BaseTrajectory.h

Framework/Geometry/BaseVector.h

Framework/Geometry/CoordinateSystem.cc

Framework/Geometry/CoordinateSystem.h

Framework/Geometry/FourVector.h

Framework/Geometry/Helix.h

Framework/Geometry/Line.h

Framework/Geometry/Point.h

Framework/Geometry/QuantityVector.h