In Sentry, when an `ActionController::InvalidAuthenticityToken` error
occurs, the breadcrumbs mention that before hitting the error, the user
clicked on one of those links.
Unfortunately we don't know which one. For debugging purposes, adding
classes to the links should allow us to see which links users are
navigating to.
it follows service-public.fr structure
- remove extraneous footer-link class
- remove extraneous space with `>` haml weird stuff
- homogenize json-style hash
- merge classes on ul
- use pseudo element for eye candy
