GitLab

- Add a theme component "book-overrides" to centralize Hugo Book theme customizations
- Copy "docs" templates to "_default" to avoid placing a "type: docs" param on each frontmatter
- Force home page to use "_default" template to prevent silent errors when updating Hugo Book
- Neutralice every bit of possible JavaScript by overriding libraries with empty files
- Remove Spanish i18n, since it's been upstreamed
- Remove mobile-header.html, since it's no longer used, and upstream has implemented the same behaviour
- Remove empty "static" folder

Home page type needs to be docs to be rendered