[Exchanges][CPU Overload] ccxt throttle related CPU overload

[GuillaumeDSM]

Due to ccxt bucket algorithm default refresh rate (1ms), when multiple pairs are activated on many exchanges, CPU can get overloaded.
This seams to happen much more often on Windows (starting from 10 pairs with kline activated on 2 exchanges).

For now we investigate to figure out if it happens more often than this specific Windows case.

possible fix:
in exchanges/connectors/ccxt_exchange.py, before instantiating the ccxt exchange:

ccxt.Exchange.tokenBucket = {
    "delay": 0.016
}