Integrate DataHighway transaction hash into block explorer

[ltfschoen]

After we provide the user with the transaction hash https://github.com/DataHighway-DHX/faucet/blob/master/helpers/contractDhx.js#L90, show them how to use it in a block explorer like polkascan.io (they said they don't havre sufficient resources to list any chain other than Polkadot and Kusama) or subscan.io (requested listing end June 2020 and awaiting response)

We already have that link for browsing Ethereum transactions on etherscan.io