Review and fix IAOs

[lweisburn]

Check and fix IAO/PAO code

• Clean localization code, removing redundant code. Allow for more general localization input options
• Expose IAO attributes, so that they are no longer hard-coded, and controllable by the user
• Fix IAO with non-symmetric orthogonalization (i.e. IAO-Boys, IAO-PM, IAO-ER)
• (TODO: Check/fix frozen core and valence-only, as they deal with the IAO/PAO code)
• (TODO: Add tests to the localization code)

[lweisburn]

In reviewing periodic code, this became a more extended change than intended (sorry)!

The kbe/lo.py and kbe/lo_k.py spread out different functions that are all contained in molbe/lo.py. Further, a lot of these functions are identical. As such, I moved the unique functions between the molecular and periodic code to molbe/lo.py and kbe/lo.py, respectively, and placed the redundant shared ones in shared/external/lo_helper.py.

[lweisburn]

Also, important note I want to leave here:

The frozen core procedure is performed differently (at least for IAOs) between the molecular and periodic codes.

In the molecular code, all orbitals are localized together, before the frozen core is identified and removed (from the localized orbitals).

In the periodic code, the frozen core is removed and treated/localized separately from the start.

I will add some warnings to the code to make sure this is very clear