Rename document_templates setup profile folder to opengever_content.

This helps indicating that all initial documents must be imported with a
separate pipeline to have correct initial document versions.
Use new office document templates.
Improve example content profile.
Use tokenized list for additional_profile configuration.
Extract emtpy document templates to separate profile.
Rename ogds import options, use ogds-sync instead of user import.
Improve configuration registry docstrings and variable names.