new doxygen groups hardParticle & legacyGrating

Core/HardParticle/FormFactorAnisoPyramid.cpp

Core/HardParticle/FormFactorAnisoPyramid.h

Core/HardParticle/FormFactorBox.cpp

Core/HardParticle/FormFactorBox.h

Core/HardParticle/FormFactorCone.cpp

Core/HardParticle/FormFactorCone.h

Core/HardParticle/FormFactorCone6.cpp

Core/HardParticle/FormFactorCone6.h

Core/HardParticle/FormFactorCuboctahedron.cpp

Core/HardParticle/FormFactorCuboctahedron.h

Core/HardParticle/FormFactorCylinder.h

Core/HardParticle/FormFactorDodecahedron.h

Core/HardParticle/FormFactorEllipsoidalCylinder.cpp

Core/HardParticle/FormFactorEllipsoidalCylinder.h

Core/HardParticle/FormFactorFullSphere.h

Core/HardParticle/FormFactorFullSpheroid.cpp

Core/HardParticle/FormFactorFullSpheroid.h

Core/HardParticle/FormFactorHemiEllipsoid.cpp

Core/HardParticle/FormFactorHemiEllipsoid.h

Core/HardParticle/FormFactorIcosahedron.h