Create testnetify script

[hochiw]

• Implement script for testnetifying the mainnet state
• Tested by running it against an actual mainnet snapshot exported genesis file, which yielded no errors

refs oursky/likecoin-chain#258

[elise-ng]

@rickmak can you help submit upstream? & we should ping other dev teams for awareness

[rickmak]

Sent to upstream https://github.com/likecoin/likecoin-chain/pull/83