Auto register new account should be seperated from Self-registration setting

[truong-hua]

By default, most of time you will would like users in your company to login and auto generate new account not existed. However, enable self-registration will also enable the registration form so external users can fill and of course automatic activation can not be chosen in the self-registration setting because people who fill in the registration form will be able to access the redmine rather than only the google authorized accounts.