email verification - apply the verification status to login flow and other flows

[chenjianjx]

As a developer,

I can choose between two schemes concerning verification status

1. VERIFICATION_REQUIRED: Without email verified, a user can't even login. They may not be able to something else.
2. VERIFICATION_NOT_REQUIRED: Without email verification, the user can still login

To be more specific,

Feature	scheme = VERIFICATION_REQUIRED	scheme = VERIFICATION_NOT_REQUIRED	More
Register with email/password	An verification email will be sent. The user will NOT be automatically logged in	An verification email will be sent. The user will be automatically logged in
Login with email/password	An verification email will be sent. Login unsuccessful	Login successful
Register/Login with social account	Login successful	Login successful	In this case the email verification status is alway "verified"
Request for random login code	An verification email will be sent. "Please verify your email first"	Allowed
Login using random login code	N/A - The user won't have any	Login successful