Ethstats operator SBAT block stats submission on a per-node basis

[timmoreton]

• TLS proxy
• Token based auth
• Figure out best approach to integrate this with 'elected validators' in Ethstats operators SBAT receive stats from all elected validators #458 - maybe they get a single global token.

[diminator]

With the changes made for #458, operators have a "trusted" list of nodes that they accept upon authorization. Stats are also signed for non-repudiation. However, there's no handshake protocol, so nodes could sniff and re-submit packages of trusted nodes. This would allow them to occupy a connection, but they won't be able to change the signed content

There's a "blocked" list in the ethstats operator, that can hold IP addresses.