Dynamic localization for menus and logo click

- Instead of using `config/_default/menus/*.toml`, this allows the use of a single `menu.toml` with `identifier = '...'` and translations in `i18n/*.toml`, as specified in https://gohugo.io/content-management/multilingual/#dynamically-localizing-menus-with-i18n
- Clicking the logo will go to the landing page while remaining in the chosen translation