Improve order and authorization schema

[aarongable]

Design goals:

• authorizations can have profiles associated with them, so we can control cross-profile authorization reuse
• tables should have a single primary key and no additional indices, to make them easy to migrate to key-value storage in the future
• tables should not have auto-increment IDs, to make them easy to migrate to sharded storage in the future
• the table containing (large, blobby) validation records should be append-only, rather than adding huge blobs to pre-existing rows in the authz table like we do today