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>
I think it is a good idea.

so you are proposing here that ```OAUTHCLIENT_SESSION_PERMANENT_LOGIN``` becomes a dict with keys being client_ids and then True or False for each of them instead of a common  ```OAUTHCLIENT_SESSION_PERMANENT_LOGIN=True``` right?