Fix logic to handle multiple outputs in ExplorerWallet.buildTXHex()

[daviortega]

Motivation

Allow ExplorerWallet.sendTx() to handle multiple outputs

What did I do?

1. I removed a logic to manually handle outputs and change.
   It seemed unnecessary since the bitcoinjs-lib appears to handle messy outputs just fine.

2. I removed an Error thrown if among the outputs from buildInputsAndOutputs() an output had no address.
   It seems that buildInputsAndOutputs will always pass the "change" output without an address attribute.
   This was fixed for transactions with only one output by the logic I removed above but it fails with multiple outputs.
   Instead, I add the p2pkh address to the "change" and removed the error.

3. I added tests for multiple outputs transaction in the integration test suite.
   I made sure previous tests that seem to use this logic still passes.

4. I also ran npm run code-format which made the other change in the code that is unrelated to this PR - but it makes the npm test pass now.