use more granular msg dict for buy/sell notifications

freqtrade/rpc/rpc.py

@@ -5,6 +5,7 @@ import logging
 from abc import abstractmethod
 from datetime import timedelta, datetime, date
 from decimal import Decimal
+from enum import Enum
 from typing import Dict, Any, List
 
 import arrow
@@ -19,6 +20,15 @@ from freqtrade.state import State
 logger = logging.getLogger(__name__)
 
 
+class RPCMessageType(Enum):
+    STATUS_NOTIFICATION = 'status'
+    BUY_NOTIFICATION = 'buy'
+    SELL_NOTIFICATION = 'sell'
+
+    def __repr__(self):
+        return self.value
+
+
 class RPCException(Exception):
     """
     Should be raised with a rpc-formatted message in an _rpc_* method
@@ -33,11 +43,6 @@ class RPCException(Exception):
     def __str__(self):
         return self.message
 
-    def __json__(self):
-        return {
-            'msg': self.message
-        }
-
 
 class RPC(object):
     """