2FA controller cleanup (#2296)

* Add spec coverage for settings/two_factor_auth area

* extract setup method for qr code

* Move otp required check to before action

* Merge method only used once

* Remove duplicate view

* Consolidate creation of @codes for backup

* Move settings/2fq#recovery_codes to settings/recovery_codes#create

* Rename settings/two_factor_auth#disable to #destroy

* Add coverage for the otp required path on 2fa#show

* Clean up the recovery codes list styles

* Move settings/two_factor_auth to settings/two_factor_authentication

* Reorganize the settings two factor auth area

Updated to use a flow like:

- settings/two_factor_authentication goes to a #show view which has a button
  either enable or disable 2fa on the account
- the disable button turns off the otp requirement for the user
- the enable button cycles the user secret and redirects to a confirmation page
- the confirmation page is a #new view which shows the QR code for user
- that page posts to #create which verifies the code, and creates the recovery
  codes
- that create action shares a view with a recovery codes controller which can be
  used separately to reset codes if needed

config/locales/zh-CN.yml

@@ -269,7 +269,7 @@ zh-CN:
     export: 数据导出
     preferences: 首选项
     settings: 设置
-    two_factor_auth: 两步认证
+    two_factor_authentication: 两步认证
   statuses:
     # Hey, this is already in a web browser!
     open_in_web: 打开网页
@@ -286,7 +286,7 @@ zh-CN:
   time:
     formats:
       default: "%Y年%-m月%d日 %H:%M"
-  two_factor_auth:
+  two_factor_authentication:
     code_hint: 请输入你认证器产生的代码，以确认设置
     description_html: 当你启用<strong>两步认证</strong>后，你登录时将额外需要使用手机或其他认证器生成的代码。
     disable: 停用