Implement Ethereum (cryptocurrency) support

[monicanagent]

Overview

Prior to supporting (updated) smart contracts support for Ethereum as a standard cryptocurrency must be implemented.

As with previous cryptocurrency integrations the aim is to support both full desktop client and light client (remote API) functionality.

Details

Implementation details should follow existing adapters. Specifically, functions makeNewWallet, getDerivedWallet, getBlockchainBalance, sendTransaction, updateTxFees, and cashoutToAddress must be implemented in a currency-agnostic way.

Note that both native and light client implementations will be extended to facilitate smart contract publishing and interactions.

The BitcoinCoreNative adapter can be used as a reference for the desktop client implementation and an extending implementation such as the BlockstreamAPI adapter can be used as a reference for the light client (remote API) implementation.

The desktop implementation should use the cross-platform Geth client: https://geth.ethereum.org/downloads/

The Web3.js library can be used to process smart contracts/interactions and interface with clients in Node.js and possibly the browser: https://github.com/ethereum/web3.js/

The light client may use any (combination) of the following candidate API services but priority should be given to any that don't require access tokens / registration:

https://cinder.cloud/ethereum-contract-api/documentation (full token-less API appears to be supported)
https://www.myetherapi.com/ (full token-less API appears to be supported)
https://www.npmjs.com/package/etherest (full token-less API appears to be supported)
https://api.aleth.io/v1/docs?utm_source=devportal (may require access token)
https://etherscan.io/apis (requires access token)
https://www.blockcypher.com/dev/ethereum/ (requires access token)
https://infura.io/docs (requires access token)
https://github.com/EverexIO/Ethplorer/wiki/Ethplorer-API?from=etop (limited API)