Faster campaign loading

Quite a significant change to how certificates are imported.

For batch loading using `rake generate:certificates` it doesn't wait for each certificate to finish, it queues them all up and saves the status url to a csv. If you want the final urls then you can run `rake generate:results` to fetch them and store the actual dataset urls in a csv.

Arguments have been changed as well. This is documented in the `README.md`