Improve SSL protocol and ciphersuite configuration (security).

As recommended my Mozilla security team as described on
https://wiki.mozilla.org/Security/Server_Side_TLS

Choosing options in "Non-Backward Compatible Ciphersuite":

* Disable both SSLv2 and SSLv3 protocols (leaving TLSv1 and up).
* Set stronger ciphersuites.
* Prefer server advertised ciphersuites over client.
Merge pull request #52 from gertvdijk/sslciphers

Improve SSL protocol and ciphersuite configuration (security).