Since there is no demo or us site anymore we can simplify the structure
somewhat by moving the sandbox one directory up

Example sites now sit in their own folder (sites) for easier
organisation.

This allows members of the public to play around with the dashboard
site.

The session object now has methods for recording that shipping isn't
required for a given order.

It handles the situation where there is no profile model too, and
dyncamically builds a profile and user form

Also had to create from migrations within the sandbox version of
shipping to keep South happy.