Add the function for login from third party services

1. This PR only contains the login by Weibo and it's configurable, the example is in application.yml.example.
2. If user register by identity,  it can also connect with third party service(Weibo).
3.  If user only login from third party service(Weibo), he/she should could setup email.
4.  If user only login from third party service(Weibo), he/she should could also can setup the password for his/her account.
5. User can unconnect fromt he third party service(Weibo).
6. The architectural make people very easy to add any other third party service for login.

创建不了. 因为 email 是相同的...
validates :email, presence: true, uniqueness: true, email: true