prefer c'tor over fct createIdentity

Sample/HardParticle/FormFactorFullSphere.cpp

Sample/Particle/IParticle.cpp

Sample/Particle/MesoCrystal.cpp

Sample/Particle/Particle.cpp

Sample/Particle/ParticleCoreShell.cpp

Sample/Scattering/Rotations.cpp

Sample/Scattering/Rotations.h

auto/Wrap/libBornAgainSample_wrap.cpp

auto/Wrap/libBornAgainSample_wrap.h