Update French locales (settings, ToS, & co) (#4261)

* add fr-FR locales to the landing page

* moar french locales

* terms of service/privacy policy

* remove un-used locales in the client (yarn manage:translations)

* update french locales in the client

* remove duplicate locales in fr.yml

* fix typos per PR comments in fr.yml

* put back default messages

* translate untranslated keys on the client

* add "push" after notifications

* correctly ident ToS in fr.yml