added a logout method that properly invalidates the user's session.
(This fixes a bug where it was possible to login with the wrong password
after once successfully loging in because the users data was still in
the session cache)

also removed all the uses crap from faces-config.xml. It appears we
don't need any of the "link-connections" and pages because we need
custom methods for almost everything anyway (like invalidating session
on logout, and validating login data etc.)