RPC: allow to optionally pass token address instead of the color

[troggy]

Overview

The common pattern had evolved when using getUnspent RPC:

const color = await rpc.getColor('0x1234...');
const utxos = await rpc.getUnspent('0x5678...', color);

Suggesting to change the color parameter of all the RPC to colorOrAddress, so we can do like that:

const utxos = await rpc.getUnspent('0x5678...', '0x1234...');

Scope

Change the following RPC to support colorOrAddress:

• getUnspent
• getUnsignedTransferTx

Deliverables

• code
• unit tests