#30 Auto-login on different computers

[Wouter Demuynck]

Right now, you can only log in from one computer at a
time. When a user logs in, a cookiekey is generated and
stored in the database as well as in the cookie on the
clients computer.

It would be nice to have the ability to log on from
multiple computers at once:

- customizable amount of login keys allowed (e.g. 2)
- table with {userid, cookiekey, last visit}
- when one logs in explicitly, a new cookiekey is
generated that overwrites the oldest entry
- when logging in implicitly, all cookiekeys for the
user should be checked for a match