Fixes to archive query. Pythonlib documentation. #699, #704.

docs/api.md

docs/pythonlib.md

examples/archive/archive_query.py

examples/archive/authenticated.py

examples/archive/client.ipynb

examples/archive/client.py

examples/archive/client_workflows.py

examples/parse.py

mkdocs.yml

nomad/client/archive.py

nomad/datamodel/datamodel.py

nomad/metainfo/metainfo.py

nomad/mkdocs.py

tests/metainfo/test_sections.py