fix(trader): Ensure consolidation of only same-currency trades

Changes include:
* unbinding _private_, and pure methods from prototype of a `Trader` object:
  * `Trader.prototype._findExchange` => `findExchange`,
  * `Trader.prototype._findTicker` => `findTicker`,
  * `Trader.prototype._findTrader` => `findTrader`,
  * `Trader.prototype._findWallet` => `findWallet`.

* Some local variables renamed to improve readability:
  * `tradeRec` => `consolidatedTrade`
  * `tickerExchangeCode` => `tickerName`,
  * `tickerExchangeConfig` => `tickerConfig`,
  * `tradeExchangeCode` => `traderName`,
  * `tradeExchangeCode` => `traderConfig`,
  * `transferExchangeCode` => `walletName`,
  * `transferExchangeConfig` => `walletConfig`.

* Since addition is commutative and order of looping doesn't matter: `while (true)` loop changed to `for..in`,
* `consolidateOther` and `otherCurencies` are used to consolidate if other currencies occur in queue.

Hmm, interesting question. Ultimately, we're checking the current BTC exchange rate when we execute the trade on the exchange, and I think the currency pair conversion should be done at the time we execute the trade of the exchange, as well. It doesn't really matter what the exchange rate was at the time of the user transaction, what matters is what the exchange rate is at the time we're doing the trade on the exchange, because if we ask for too low a rate, the trade won't go through.

I suppose if you have both USD and EUR balance on the exchanges, you'd ideally want to make USD trades off of the USD balance and EUR off of the EUR balance. That could be a good feature to tackle later, but I think it would take a lot of thought to get it right and manage the balances correctly.

It's much simpler to  assume the operator only has one target currency balance, and convert everything to that. I'd like to start with that, and if we want to add in multiple currency balances later, we'll put in the time to design that. Since we're sticking with a single target currency, let's simplify and not bother with the otherCurrencies.