Allow for no keys

[bneradt]

Currently, proxy-verifier will fail parsing and will not send traffic if it finds any transactions without a key. This is probably good in most cases to avoid surprising the user with unexpected traffic (502s, say). But it would be good to allow them to do this if they know what they are doing. Perhaps setting --format "" should be allowed to avoid non-existent key checks.

[bneradt]

Gah...connectivity issue created two issues. This is replaced with #91