Implement null auth backend

Authentication/authorization backends belong in haas/auth_mechanisms .  There
is CLI support, based on requestlib's pluggable authentication mechanism.
Add database-backed user/password authentication scheme

In this model, there are three kinds of groups of people that can be allowed
to perform an operation: anyone; anyone with access to the projecct, as well
as administrators; only administrators.  Right now, which operation has which
property is not tunable.

In implementing this, operations that anyone can perform have had their
'authorize' checks removed entirely.  This is not a very consistent way to do
this.  It also has the property that even unauthenticated users can perform
the action, which (depending on circumstances) may be desirable or not.

Also included is a script to create an initial admin user.