Disable a user account

[jessevondoom]

We need a way to disable a user account in the multi-user version. For now it can be as simple as a flag in the people table — potentially even using the "is_admin" flag to suspend their publishing and login rights.

[jessevondoom]

Closing this issue because we can simply set the admin flag to 0 and a user account is effectively suspended. We need to keep this in mind as we publish pages — that pages belonging someone with no admin flag should simply not be rendered — but otherwise this is an easy fix.