Move C2 data structures under ParticleDescriptor

src/cluster/cluster.cpp

src/include/Commons.h

src/include/inclu_subs.h

src/include/sph_subs.h

src/libnptm/Commons.cpp

src/libnptm/inclu_subs.cpp

src/libnptm/sph_subs.cpp

src/sphere/sphere.cpp