[proxy/tls] Update supported TLS versions and cipher suites

[dcarbone]

The current list of supported TLS versions is as follows:

var tlsver = map[uint16]string{
    tls.VersionSSL30: "ssl30",
    tls.VersionTLS10: "tls10",
    tls.VersionTLS11: "tls11",
    tls.VersionTLS12: "tls12",
}

We should do the following:

1. Remove tls.VersionSSL30 from the map
2. Add tls.VersionTLS13 to the map
3. Add a deprecation warning when tls.VersionTLS10 or tls.VersionTLS11 is selected.