Geometrical core improvement: ignore cores, owned by one SS element * add argument ignore_one_ss to geometrical_cores() method (=True) * add argument ignore_one_ss to other methods of structure, calling geometrical_cores() (=True) * add command line option to blocks3d, geometrical_core, pair_cores (=False) * remove xyz_only=True from pair_cores, since secondary structure determiner needs structures to be loaded This have not been tested! close #119