allow setting the preferred feeSize

[jojobyte]

When sending a very small amount 0.0001 as a full transfer, Dash Insight API failed with a 400 complaining the fee of 191 was less than the minimum 192.

This allows overriding the default selected fee from fee.min (191) to fee[feeSize].

feeSize can be a string value of min, mid, or max corresponding to the values returned by DashTx.appraise(...)

let txDraft = await dashwallet.legacy.draftTx({
  utxos,
  inputs,
  output,
  feeSize: 'max',
})

[riongull]

@coolaj86, as discussed, go ahead and fix the underlying issue that's causing the error rather than giving users an option to select fees.

[coolaj86]

Replaced by:

• feat: move legacy draft & finalizeAndSign from DashWallet.js to here DashTx.js#35
• ref: externalize storage from legacy tx functions #49

The root cause was essentially this:

  let lastTime;
  for (;;) {
    // ...
-   lastTime = thisTime;
    if (thisTime === lastTime) {
      break;
    }
+   lastTime = thisTime;
    // ...
  }

But there were a tonne of other bugs in the code.