Merge `ase-koopmans` with `ase`

[elinscott]

Several functionalities within ase-koopmans are deprecated.

In order to minimize maintenance, we should merge ase-koopmans with the official version of ase. (Easier said than done, but will be worthwhile in the long-term...)

[elinscott]

As an interim measure, elinscott/ase_koopmans#68 has added detection of deprecated code in ase-koopmans