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. It felt natural to add them to it.

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.