State block version 2 activation

[zhyatt]

Summary
Support for the new state block (version 2) to be added. Activation will be done using canary blocks to start the generation, parsing and publishing of the blocks (de-peering earlier version nodes), followed by a new distribution of epoch blocks to ensure all accounts in the ledger contain a block with the proper version.

Related Links

• Implementation covered in PR #2899
• Forum discussion: https://forum.nano.org/t/new-state-block-design/892/21