Revert part of "mv pseudonyms and db split to separate "data separation" page"

See merge request !81

General update

See merge request !79

improve role descriptions

See merge request !80

This reverts parts of commit f9b2e260.

The technical details fit better in the secrutiy chapter because it is
supposed to give a quick overview of security measures implemented in
castellum.

Document general pseudonyms

See merge request !78

expand 2FA documentation

See merge request !77

inspired by https://docs.mpcdf.mpg.de/faq/2fa.html

Add example for totp apps

See merge request !76

document two factor authentication

See merge request !75

change "attribute" to "recruitment attribute" in UI

See merge request !74

fix typo

See merge request !72

see castellum!1941

document study approval issue

See merge request !70

add guide for resetting user tokens

See merge request !71