Block possibility to change of user visibility

[ntarocco]

In the context of CERN and CDS, we should not allow that a user can change the profile visibility. This is because, after a login, you can already find emails/other info in other services, e.g. Phonebook, Indico. It makes sense to always being able of finding search users for logged in users.

Assumptions: the /api/users endpoint and the /api/names endpoint are restricted

1. block the UI and the backend that allows to change user profile and email visibility
2. change the OAuth integration and the maybe the users sync to set them visible