[feature] harden service node requirements

[rikublock]

Service nodes are the corner stones of the Blocknet network as they provide all sorts of services. However service nodes (and to some extend the service node list) aren't all that reliable. Therefore, I propose to hard harden the following requirements:

• uptime: should always be online/running (reliability)
• static IP: should have static IPv4 address (ideally also IPv6) - linked to a snode pubkey
• list: deterministic snode list (global consensus)
• proofs: sndoes could test other snodes to ensure uptime, validity of returned data, etc.
• etc.