Change auth storage to allow a raw username to be stored and read

Summary:
We can override the encryption and auth process of the stored cookie data.
This adds a function that lets us know if a user is probably logged in, and

Test Plan: Look and hope

Reviewers: brooke

Reviewed By: brooke

Maniphest Tasks: T131

Differential Revision: http://phabricator.cubex.io/D28