Improve off-chain client development setup experience

[pdyraga]

Currently, the local development setup includes only Ethereum node. Testing sweeps and redemptions locally is not possible which makes the development cycle longer.

Ideally, as a tBTC developer, I'd like to:

• Have Ethereum network running locally with the contracts deployed and initialized.
• Have Bitcoin network running locally OR in the dev cloud OR use Bitcoin testnet (*).
• Have the difficulty maintainer running locally and connected to Bitcoin and Ethereum.
• Have the dashboard running locally and connected to Bitcoin and Ethereum.
• Be able to run several client instances connected to Ethereum and Electrum clients and easily update the code.
• Nice to have: some kind of a block explorer allowing to inspect the state of Bitcoin/Ethereum networks.

(*) Getting testnet Bitcoin is not straightforward.