Replace default bitcoind wallet with multiple purpose specific wallets

[jotapea]

The current bitcoind tests implementation use a single "all encompassing" default wallet client which is used for many purposes. The goal is to split this one client/wallet into:

• default client:

  • Only to be used for non-transaction wallet functionality (like: getBlockchainInfo, createWallet, listWallets, decodeRawTransaction, loadWallet, unloadWallet, getBlockCount?).
    • All code that uses the listWallets call needs to be updated to now consider the addition of new wallets.
    • A single getBlockCount function has been kept for the default wallet (TODO?).

• outside wallet:

  • Represents the outside world, which is required for simulating transactions in tests.
  • This is replacing all tests from the original "" (unnamed) wallet that do transactions (generate, receive or send coins).

• hot wallet:

  • FUTURE use, will eventually replace the lnd onchain wallet.
  • The scope of this one at this phase is only to be added as another wallet in the tests.

[jotapea]

@nicolasburtey PR #354 is ready.