Dynamically load default Block and Transaction classes

[taustin]

This might have to wait on converting to ES6 modules.

[taustin]

More details:

The Block and Transaction classes have been made configurable in order to make SpartanGold more extensible.

However, that means the these classes must be specified, even if the default implementations are perfectly fine.

Here is how driver.js currently creates the genesis block:

// Creating genesis block
let genesis = Blockchain.makeGenesis({
  blockClass: Block,
  transactionClass: Transaction,
  clientBalanceMap: new Map([
    [alice, 233],
    [bob, 99],
    [charlie, 67],
    [minnie, 400],
    [mickey, 300],
  ]),
});

Instead, it should look like:

// Creating genesis block
let genesis = Blockchain.makeGenesis({
  clientBalanceMap: new Map([
    [alice, 233],
    [bob, 99],
    [charlie, 67],
    [minnie, 400],
    [mickey, 300],
  ]),
});