feature：1.加群功能插件化；2.成员变更不监听消息，使用定时检查策略；

message_util.py

@@ -50,7 +50,7 @@ class MessageUtil:
             self.wcf.send_text(f"{msg}", receiver, at_list)
         else:
             self.LOG.info(f"To {receiver}: {ats}\r{msg}")
-            self.wcf.send_text(f"{ats}\n\n{msg}", receiver, at_list)
+            self.wcf.send_text(f"{ats}\n{msg}", receiver, at_list)
 
     def send_file(self, file_path: str, receiver: str) -> None:
         """