Vote storage

[zhyatt]

Summary
Allow nodes to be configured for storage and republishing of Principal Representative votes for blocks.

What problem would be solved by this feature?
Currently, any node that isn't able to observe enough votes to confirm a block from the initial vote publishing and rebroadcasting done during elections send all vote requests directly to Principal Representatives, who must spend resources responding (and sometimes regenerating the votes). This can reduce the network throughput during heavy traffic times as nodes falling out of sync rely heavily on PR responses to catch them back up. Vote storage allows secure response to vote requests by non-PRs, thus reduces PR load and is anticipated to help keep throughput maximized during high traffic times.

Dependencies

• Network overlay (DHT-based) - how votes are storage and requested would be based on network structures established by the network overlay implementation