Updated documentation.

docs/.static/css/custom.css

docs/api.rst

docs/components.png

docs/conf.py

docs/data.png

docs/dev_guidelines.rst

docs/index.rst

docs/introduction.md

docs/introduction.rst

docs/proc.png

docs/reference.rst

nomad/api/auth.py

nomad/coe_repo/__init__.py

nomad/coe_repo/upload.py

nomad/coe_repo/user.py

nomad/datamodel.py

nomad/dependencies.py

nomad/files.py

nomad/infrastructure.py

nomad/normalizing/__init__.py