Reorientation settings are in lattice but make more sense in unitcell settings

[drjbarker]

We can reorient the system using settings like:

lattice : {
  orientation_axis = [0.0, 0.0, 1.0];
  orientation_lattice_vector = [1.0, 1.0, 1.0];
}

but it is not very easy to then split the unit cell into a separate config because for example the exchange interactions must be calculated after the rotation so they rely on the lattice settings as well as unitcell when really they only need to depend on the unitcell.