unspentoutput constructor does not work with cashaddr

[dfoderick]

The class unspentoutput does not work with cashaddr because the following line assumes it is a legacy address and fails with Error: Checksum mismatch in Base58Check.

const address = data.address ? new Address(data.address) : undefined;

This constructor is called during Transaction.from so it is a major use case.

See the following branch with a test that fails.
https://github.com/the-bitcoin-token/bitcoin-source/compare/unspentoutput_cashaddr?expand=1

There are several ways to fix:

• Fix the Address constructor to work with cashaddr
• Change UnspentOutput to use Address,fromString