Add kucoin exchange subclass

Kucoin has some specific orderbook restrictions

closes #4723

freqtrade/exchange/kucoin.py

@@ -0,0 +1,24 @@
+""" Kucoin exchange subclass """
+import logging
+from typing import Dict
+
+from freqtrade.exchange import Exchange
+
+
+logger = logging.getLogger(__name__)
+
+
+class Kucoin(Exchange):
+    """
+    Kucoin exchange class. Contains adjustments needed for Freqtrade to work
+    with this exchange.
+
+    Please note that this exchange is not included in the list of exchanges
+    officially supported by the Freqtrade development team. So some features
+    may still not work as expected.
+    """
+
+    _ft_has: Dict = {
+        "l2_limit_range": [20, 100],
+        "l2_limit_range_required": False,
+    }