Merge branch 'issue/209' into 'develop'

config/config.exs

config/description.exs

config/test.exs

docs/API/admin_api.md

docs/API/pleroma_api.md

docs/configuration/cheatsheet.md

lib/pleroma/mfa.ex

lib/pleroma/mfa/backup_codes.ex

lib/pleroma/mfa/changeset.ex

lib/pleroma/mfa/settings.ex

lib/pleroma/mfa/token.ex

lib/pleroma/mfa/totp.ex

lib/pleroma/plugs/ensure_authenticated_plug.ex

lib/pleroma/user.ex

lib/pleroma/web/admin_api/admin_api_controller.ex

lib/pleroma/web/auth/pleroma_authenticator.ex

lib/pleroma/web/auth/totp_authenticator.ex

lib/pleroma/web/common_api/utils.ex

lib/pleroma/web/oauth/mfa_controller.ex

lib/pleroma/web/oauth/mfa_view.ex