Support testnet use

[libitx]

moneybutton/bsv does not automatically parse a testnet address - it must be explicitly instantiated with Address.Testnet().

To support testnet there should be a configuration flag and instantiate from the correct class at the following places:

• https://github.com/libitx/txforge/blob/master/src/forge.js#L87
• https://github.com/libitx/txforge/blob/master/src/forge.js#L97
• https://github.com/libitx/txforge/blob/master/src/forge.js#L203

[libitx]

Testnet is supported in v2