Added formal models for most annotations and updated the schema docs.

docs/schema/basics.md

docs/schema/elns.md

docs/schema/suggestions.yaml

gui/src/metainfo.json

nomad/cli/admin/run.py

nomad/cli/dev.py

nomad/datamodel/metainfo/__init__.py

nomad/datamodel/metainfo/annotations.py

nomad/datamodel/metainfo/eln/annotations.py

nomad/metainfo/metainfo.py

nomad/metainfo/util.py

nomad/mkdocs.py

nomad/parsing/tabular.py

tests/datamodel/test_schema.py

tests/metainfo/test_metainfo.py

tests/metainfo/test_yaml_schema.py

tests/parsing/test_tabular.py