There is no easy way to edit the values sent
to newly generated users from oauth_signup.
In some cases,
the mapping from an oauth provider can be different.
* ex: login is something other than email
In other cases,
there are additional fields in res_users added by a module
* ex: firstname and last name in `partner_firstname`
This factorization allows modules inheriting from `auth_oauth_signup`
to alter values sent to the copy of Template User.
This means smaller changes to the default behaviour
and the ability to properly inherit
(multiple times if needed)
this module without losing needed behaviour.
Closes#2355
Sandy Carter
Denis Ledoux
Olivier Dony
Raphael Collet