- Removed disable button from /profile/account
- Added disable button to /profile/two_factor_auth
- Changed 2FA breadcrumb from 'User Settings > Account > Account' to 'User Settings > Account > Two-Factor Authentication'

And link to it from where you change your username.

Previously the user could not delete his own account unless signup was
enabled in the global settings. This was due to the fact that deleting
the user would also delete the issues and other items associated to him.
Deleting an user does not destroy essential data anymore, for this
reason we removed the `signup_enabled?` check.

`breadcrumb_title` is then overriden when needed

Closes #20918

+ Add a partial for displaying user deletion guidance

- Add a `destroy_user` ability. This didn't exist before, and was implicit in
  other abilities (only admins could access the admin area, so only they could
  destroy all users; a user can only access their own account page, and so can
  destroy only themselves).

- Grant this ability to admins, and when the current user is trying to destroy
  themselves. Disallow destroying ghost users in all cases.

- Modify the `Users::DestroyService` to check this ability. Also check it in
  views to decide whether or not to show the "Delete User" button.

- Add a short summary of the Ghost User to the bio.

reactivates all tests and writes more tests for it

email token be reset

The helper constructs the path for a given oauth provider since Devise 4.0 deprecated passing the provider to the omniauth authentication path.

Fixes #18110.

- Move the `TwoFactorAuthsController`'s `new` action to `show`, since
  the page is not used to create a single "two factor auth" anymore. We
  can have a single 2FA authenticator app, along with any number of U2F
  devices, in any combination, so the page will be accessed after the
  first "two factor auth" is created.
- Add the `u2f` javascript library, which provides an API to the
  browser's U2F implementation.
- Add tests for the JS components

This reverts commit 3e991230.

# Conflicts:
#	app/models/project.rb

Main idea is to keep left sidebar static so user is not confused by
changing context. Instead we put changing navigation with changing
content in one main block
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Added in disable button for 2fa

Closes #13854