Command to export the block and state data required to start a full sync at provided blockheight

[i-norden]

For https://github.com/vulcanize/issue_tracking/issues/24

• Uses Roy's concurrent state trie iterating code
• Properly segments data across ancient datastore and levelDB
• Needs to be optimized with batched trie node writing to the destination/import levelDB
• Needs unit/integration tests

[i-norden]

TODO:

• [ ] Make Roy's suggested changes
• [ ] Write and perform tests
• [ ] Possible fixes required after testing
• [ ] Modify so that code updates the "latest header" index and any other required indexes in the destination levelDB: https://github.com/ethereum/go-ethereum/blob/master/core/rawdb/schema.go#L35 aka call https://github.com/ethereum/go-ethereum/blob/master/core/rawdb/accessors_chain.go#L181

I think for the last point the only other index we need to update is https://github.com/ethereum/go-ethereum/blob/master/core/rawdb/schema.go#L38 but need to double check