Modify PDB atom name reading

This commit updates how VaspCat reads atom names from pdb files in order
to correct issues users were having with incorrect atom identification.

Now, VaspCat will preferentially extract atom names from the end of
ATOM and HETATM records as opposed to from the third column.  If atom names
are not found at the end of the line, the program will extract atoms
from column 3, omitting extraneous orientation and bonding labels.

CHANGELOG:
- Modified vaspcat/extend/filetype.py to preferentially extract pdb atom
  names from characters 77 and 78 in ATOM records.
- Changed the types of labels that filetype.py will ignore when reading
  atom names from column 3 of ATOM and HETATM records.