WIP oauthclient/accounts: permanent login support

* Sets session.permanent when then user marks 'remember me'.

* Allows configuration of oauth login to set if session should
  be permanent.

Signed-off-by: Javier Martin Montull <javier.martin.montull@cern.ch>
Ok, I see now. 

1) Do we have a good use case that where you would want to set different value per client_id? 
2) If we want to set it per ``client id``, I would not add ``OAUTHCLIENT_SESSION_PERMANENT_LOGIN`` , but instead add it to: https://github.com/inveniosoftware/invenio/blob/pu/invenio/modules/oauthclient/config.py#L68