One watchlist, its filters and digest, and the organization's allowance.
The list a creation answered with, by its id. The
same object as in the list of watchlists, under watchlist, beside the organization's
allowance. digest.sent_at is when the last digest was mailed, null until one has
been. A list of another organization and an id that never existed are both
404 not_found, and cannot be told apart.
Not counted as a call. A list read right after it was written reflects the write.