fix(trader): improved consolidation; readability improvements and cleanup

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 it's not used, and plugin interface accepts value in `satoshis` only, `fiat` property removed completely from consolidation.