Trivial user-server.

 This user-server will allow data to be retrieved, and will
allow logins to be tested.  There is still no creation functionality
and we don't use the SALT field in the database meaning only
old-school logins work - not upgraded accounts.
  Add configurable user-server URL.
  Removed numbers from TODO to avoid update-churn.
local config _can_ override default-config.
 Trivial base-class for cookie/session setup.
 Use the base-class we've just added.

 This means we get sessions, via Redis.
  Singleton helper for Redis.

  We use redis for application login-sessions.