Add UTxO endpoints

Add support to the following endpoints to the [`NodeClient`](https://github.com/arobsn/hergmes/blob/25f1093813e95ab25c321911eefae1c9cd69bc15/src/clients/node.rs#L34) module

- `GET /blockchain/box/unspent/byTokenId/{tokenId}`;
- `POST /blockchain/box/unspent/byErgoTree`.
- `POST /blockchain/balance`