validator: set EDE code if SEP does not match or DNSKEY is revoked.

If the tag and algorithm of DS and DNSKEY do not correspond, or in case
the DNSKEY is revoked, set EDE code "DNSKEY Missing".
If both match, but the algorithm is not supported, set EDE code
"Unsupported DNSKEY Algorithm".
In case RRSIGs for DNSKEY exist, but can't be validated due to a key
error, set EDE code "RRSIGs Missing".