login, DescriptorUnits

The Ark class really doesn't deal with descriptor units, while that is the intended focus of DArk. Consequently, I'd really like to move descriptor unit creation (triggered by a call to makeCabinet) up to DArk. But perhaps not today.

Now that new user registration is done, I really want to work on user login. Its just wierdly disfunctional having one without the other.

Bill