Rearrange data importing

I wanted to be able to import all of the data from redirector in production automatically on a daily basis. We're using `rake import:all` to do this, but it misses out Orgs, Sites and Hosts. So if Orgs, Sites and Hosts were added or changed in redirector, that wouldn't be applied to Transition/Bouncer.

Whilst the Transition app can now edit mappings, the canonical source for everything is still the redirector repo (and transition-stats for Hits).

I've also added cloning the transition-stats repo to `setup.sh` because it felt weird to ignore it when `rake import:all` uses it.