Continued to work on optimade and metainfo.

nomad/datamodel/base.py

nomad/datamodel/dft.py

nomad/metainfo/metainfo.py

nomad/metainfo/optimade.py

nomad/normalizing/optimade.py

nomad/parsing/backend.py

tests/app/test_optimade.py

tests/test_metainfo.py