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>
Please note that `login_user` has `remember=False` argument hence we should use it (see https://flask-login.readthedocs.org/en/latest/#flask.ext.login.login_user).