Regression from #11831

* Fix 2FA challenge not appearing for non-database users

Fix #11685

* Fix account deletion not working when using external login

Fix #11691

CSFR-prevention is already implemented but adding this doesn't hurt.

A brief introduction to Same-Site cookies (and the difference between strict and
lax) can be found at
https://blog.mozilla.org/security/2018/04/24/same-site-cookies-in-firefox-60/

TLDR: We use lax since we want the cookies to be sent when the user navigates
safely from an external site.

Fix #6816, fix #6790

* add pam support, without extra column

* bugfixes for pam login

* document options

* fix code style

* fix codestyle

* fix tests

* don't call remember_me without password

* fix codestyle

* improve checks for pam usage (should fix tests)

* fix remember_me part 1

* add remember_token column because :rememberable requires either a password or this column.

* migrate db for remember_token

* move pam_authentication to the right place, fix logic bug in edit.html.haml

* fix tests

* fix pam authentication, improve username lookup, add comment

* valid? is sometimes not honored, return nil instead trying to authenticate with pam

* update devise_pam_authenticatable2 and adjust code. Fixes sideeffects observed in tests

* update devise_pam_authenticatable gem, fixes for codeconventions, fix finding user

* codeconvention fixes

* code convention fixes

* fix idention

* update dependency, explicit conflict check

* fix disabled password updates if in pam mode

* fix check password if password is present, fix templates

* block registration if account is maintained by pam

* Revert "block registration if account is maintained by pam"

This reverts commit 8e7a083d65.

* fix identation error introduced by rebase

* block usernames maintained by pam

* document pam settings better

* fix code style

* Add confirmation step for email changes

This adds a confirmation step for email changes of existing users.
Like the initial account confirmation, a confirmation link is sent
to the new address.

Additionally, a notification is sent to the existing address when
the change is initiated. This message includes instruction to reset
the password immediately or to contact the instance admin if the
change was not initiated by the account owner.

Fixes #3871

* Add review fixes

Force SSL only cookies for remember_me, adjust confirmation
expiration time to fit with the user cleanup scheduler

* Fix #4058 - Use a long-lived cookie to keep track of user-level sessions

* Fix tests, smooth migrate from previous session-based identifier

* Add overview of active sessions

* Better display of browser/platform name

* Improve how browser information is stored and displayed for sessions overview

* Fix test

* feat: Revocable sessions

* fix: Tests using sign_in

* feat: Configuration entry for the maximum number of session activations

* Add recovery code support for two-factor auth

When users enable two-factor auth, the app now generates ten
single-use recovery codes. Users are encouraged to print the codes
and store them in a safe place.

The two-factor prompt during login now accepts both OTP codes and
recovery codes.

The two-factor settings UI allows users to regenerated lost
recovery codes. Users who have set up two-factor auth prior to
this feature being added can use it to generate recovery codes
for the first time.

Fixes #563 and fixes #987

* Set OTP_SECRET in test enviroment

* add missing .html to view file names

Do not require e-mail address changes to be re-confirmed, it's only trouble for no real benefit

POST /api/statuses                  Params: status (text contents), in_reply_to_id (optional)
GET  /api/statuses/:id
POST /api/statuses/:id/reblog

GET  /api/accounts/:id
GET  /api/accounts/:id/following
GET  /api/accounts/:id/followers
POST /api/accounts/:id/follow
POST /api/accounts/:id/unfollow

POST /api/follows                  Params: uri (e.g. user@domain)

OAuth authentication is currently disabled, but the API can be used with HTTP Auth.