VaspImmigrant calculation

VASP input and output files are read from a folder path.

1. Read VASP input files POSCAR, KPOINTS, and INCAR have to exist. POTCAR is optional because users may remove it due to its large file size.

   If POTCAR does not exist, the provided potential_family and potential_mapping parameters are used to link potential to inputs. In this case, at least potential_family has to be provided. Unless provided potential_mapping, it is generated from structure, i.e.,

   potential_mapping = {element: element for element in structure.get_kind_names()}

2. Pretend that VaspCalculation finished and files were retrieved.

3. Read VASP output files settings is passed in get_builder_from_folder(settings=settings) as a python dict.