caramel_tool --list appears slow #54

With some 1500+ CSR requests and some 20 000 certificates per request, the behaviour of caramel_tool --list becomes annoying.

This is probably because it just does "list all CSR, for each CSR fetch all Certs ordered by ...." or similar. When the correct would be "select csr, max(crt.date) group by csr " or similar query.

Reproduction:

• Generate a few thousand cert requests and insert them
• Sign each one a few thousand times
• Check the performance