Basis set orbitals are not linked to atoms in a structure

[hatemhelal]

At the point where we create each atomic orbital we effectively copy the center from each atom to use within the orbital instance. This effectively disconnects the orbitals from being associated with a particular atom and presents a few problems:

• autodiff with respect to atomic positions doesn't work out of the box
• associating orbitals with atomic level labels requires an additional mapping to be defined

One solution might be to use an atom id instead of using the atom center when creating the orbital instances.