Add session expiration 'cron' job

[grant-h]

Old sessions are left in the database after a server restart. We should create a cron job using setInterval to expire all old sessions every minute or so.

[grant-h]

Actually on second thought, all we need is to check for old sessions upon login once, expire them. For sessions that are still valid, add a setInterval callback to expire them at the proper time

[Juan-Jauregui]

If by "login" you mean "server start" then I agree that's a better solution.