Record and Expose P2P Status of the nodes

[wy]

One of the improvements over City of Zion's monitor is to track the P2P status of nodes. The difference between P2P and JSON-RPC is that P2P is needed for a node to receive and communicate blocks. Even if it is not a consensus node, it can play an important part in quickly communicating new blocks as they are finalized.

JSON-RPC on the other hand is needed for outside services (non-nodes) querying the node for information.

City of Zion's monitor checks for JSON-RPC but not for P2P. That means it suffers from two issues:

1. It misses nodes that are P2P but not JSON-RPC - so they are legitimate nodes, they just can't be queried through JSON-RPC
2. it finds nodes that are JSON-RPC but not P2P, which normally means they will have stale / old blockchain data. This is exposed in the Monitor's information, but the reason for the delay is unclear (is it because of no P2P or just some other issue)

Adding P2P is a requirement pre 1.0, and so we should treat this as a post-Hackathon clean up task.

[wy]

Working - closed.