Rework the default cipherlist.

 - Always prefer forward-secure handshakes.
 - Consistently order ECDSA above RSA.
 - Next, always prefer AEADs to non-AEADs, irrespective of strength.
 - Within AEADs, prefer GCM > CHACHA > CCM for a given strength.
 - Prefer TLS v1.2 ciphers to legacy ciphers.
 - Remove rarely used DSS, IDEA, SEED, CAMELLIA, CCM from the default
   list to reduce ClientHello bloat.

Reviewed-by: Rich Salz <rsalz@openssl.org>