Import datasets for Bittrex via CryptoCompare API

[xFFFFF]

I add to develop branch of BacktestTool (https://github.com/xFFFFF/Gekko-BacktestTool) import candles from CC API to gekko DB. So You can import bittrex datasets now. 

CC API has some limitations - only last 7 days are available to import, dont provide trades amount and wvp. Be sure does Your strategy dont use trades and wvp values!