Add charges of atoms connected to donor atoms to descriptors

[akalikadien]

This might give info on the effects that the backbone has on the first coordination sphere.
To implement this, we should first find all atoms connected to the P that are not the metal center (e.g. via openbabel or just searching within a radius around the P based on interatomic distances). Then save those indices and save those values from cclib in the final df.