Cleaned up Python bindings to restore functionality: * StaticPersistence is iterable, its nodes are usable (sign, pair, cycle) * StaticPersistence knows how to map its nodes into Filtration indices * moved PythonCmp into utils.h * minor cosmetic changes

#include <topology/chain.h>
#include "static-persistence.h"

typedef     SPersistence::Chain                     VChain;