Code-Change & error page improvement

  1. Removed the error model. But I don't know how to deal with the
  messages in i18n translation. I'll try to find a solution later.
  2. Some of the logic is incomplete. You mentioned there should be a
  navigation to '/error', but it will cause infinite loop, as that's
  already in error_controller. If we navigate in ErrorController#index,
  who's going to show the error page?