Integrate ABC module where we have abstract classes

lib/tfw/networking/server/zmq_websocket_handler.py

@@ -1,4 +1,5 @@
 import json
+from abc import ABC, abstractmethod
 
 from tornado.websocket import WebSocketHandler
 
@@ -9,7 +10,7 @@ from tfw.config.logs import logging
 LOG = logging.getLogger(__name__)
 
 
-class ZMQWebSocketHandler(WebSocketHandler):
+class ZMQWebSocketHandler(WebSocketHandler, ABC):
     _event_handler_connector = EventHandlerConnector()
     instances = set()
 
@@ -45,6 +46,7 @@ class ZMQWebSocketHandler(WebSocketHandler):
         LOG.debug('Received on WebSocket: %s', message)
         self.send_message(self.make_response(message))
 
+    @abstractmethod
     def make_response(self, message):
         raise NotImplementedError