Kraken: added endpoints costs
Kraken: added endpoints costs

We ran into rate limits due to TradesHistory calls are counting 1, but cost is 2, instead of default 1.
This will fix the rate limiter.

Costs can be found here:
https://support.kraken.com/hc/en-us/articles/206548367-What-are-the-API-rate-limits-
ccxt/ccxt,ccxt/ccxt,ccxt/ccxt,ccxt/ccxt,ccxt/ccxt