Integrate typechain to caver-js

[kjhman21]

https://www.npmjs.com/package/typechain

It would be good if we integrate typechain into caver-js.

Example usage:

  const StakingWhitelist = await ethers.getContractAt('StakingWhitelist', WHITELIST_ADDRESS)
  await StakingWhitelist.addWhitelist(whitelist)