Draft: Add draft interface of layer groups to ASE

Add draft interface to ASE for the draft python interface of spglib for the experimental layergroup implementation of spglib.

Lot's of things still need polishing and testing.

Works with spglib, which has preliminary interface https://github.com/mikaelkuisma1/spglib/tree/add-layer-group-python-interface

See also https://github.com/spglib/spglib/pull/199