Two factor authentication (#7751)

.gitignore

Changelog.md

Gemfile

Gemfile.lock

app/assets/stylesheets/login.scss

app/controllers/application_controller.rb

app/controllers/sessions_controller.rb

app/controllers/two_factor_authentications_controller.rb

app/controllers/users_controller.rb

app/helpers/application_helper.rb

app/models/user.rb

app/views/sessions/two_factor.html.haml

app/views/shared/_settings_nav.haml

app/views/two_factor_authentications/_activate.haml

app/views/two_factor_authentications/_confirm.haml

app/views/two_factor_authentications/_deactivate.haml

app/views/two_factor_authentications/_recovery.haml

app/views/two_factor_authentications/_token_form.haml

app/views/two_factor_authentications/confirm_2fa.html.haml

...views/two_factor_authentications/recovery_codes.html.haml