fhi-aims hamiltonian

[zerothi]

Describe the feature

It would be great to allow reading in fhi-aims hamiltonians. In this way we could have an all-electron Hamiltonian access point.

@ialcon here your help could be really valuable, trying to get this up and running requires knowledge on the aims side (which I don't have), and also there is plenty of code in sisl to see how to read stuff from.