Dump Structure data into file

[hghcomphys]

It is useful for saving ML-potential predictions into files.

[hghcomphys]

This was implemented by converting Structure instance to the ASE atoms and vice versa.
ASE makes it possible to read/write different file formats (see this) such as xyz, POSCAR, and pdb.
It also allows to modify atoms in the cell and save back the results into the Structure.