user gomail and new activate account email tpl

- #1496: fallback plain text
- #1002: add date header
- #913: fix encoding of header

conf/locale/locale_en-US.ini

@@ -160,6 +160,11 @@ invalid_code = Sorry, your confirmation code has expired or not valid.
 reset_password_helper = Click here to reset your password
 password_too_short = Password length cannot be less then 6.
 
+[mail]
+register_success = Register success, Welcome
+activate_account = Please activate your account
+activate_email = Verify your e-mail address
+
 [modal]
 yes = Yes
 no = No