Migration to the new Poloniex API [Public endpoints only] (#795)

* Add CryptoUtility.PrecisionToStepSize Precision to step size convertor. For example, precision of 5 would return a step size of 0.00001. * Add ExchangeAPIExtensions.ParseOrderBookFromJTokenArray Common order book parsing method, some exchanges (Poloniex) use single array for the whole depth (price and qty) like "asks" : [ "24500.00", "0.024105", "24513.16", "0.611916", "24514.27", "0.001987"] * Add CryptoUtility.SecondsToPeriodStringLongReverse Convert seconds to a period string, i.e. SECOND_5, MINUTE_1, HOUR_2, DAY_3, WEEK_1week, MONTH_1, YEAR_1 etc. * Migration to the new Poloniex API [Public endpoints only] * Add incomplete request and signature for Poloniex Can't come up with a working solution.

Author: BZ-CO