See the latest update to the BEP-42.

The logic is triggered by the last election vote.

• Generate a new chain ID and update the currently set value.
• Turn on a flag that prevents BigchainDB from accepting new transactions.
• Turn the flag off upon receiving the matching chain_id in InitChain.
• Update the ABCI interface (e. g. the info command) to return height - chain offset to Tendermint instead of just height.