ERC777 contract usage example

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Description:

This is simplest example code which uses ERC777 contract and ERC777Hooks (Sender, Recipient) to transfer tokens and emits Hooks events.

Code does:

1. Deploys ERC1820 contract if not yet exist to private ethereum based blockchain.
2. Deploys*** ERC777 contract
3. Deploys*** ERC777Recipient, ERC777Sender contracts
4. Creates Client (ETH account) on demand
5. Makes a check that tokens were transferred to Client
6. Logs received events: 'TokensReceivedCalled', 'TokensToSendCalled'

Tested using locally running Hyperledger Besu - version

Solidity contracts were taken from Openzeppelin

Web3j - as ethereum JSON-RPC java library

*** - creates New contract if address is not explicitly set in 'application.yml' file under 'netContracts/name/address' section