Link to privacy notice where appropriate

[karolina-siemieniuk-morawska]

The CERN Office of Data Privacy recommends us to display a link to the privacy notice after users log in so they get informed of our use of their personal information. We don't redirect to a profile page after login, so there's no immediately obvious place to add such a link. We need to identify where such a link would be appropriate and add the link.

Moved from: inspirehep/inspirehep#2392