成员的完整列表，这些成员属于 NIMQChatSystemNotification,包括所有继承而来的类成员

callback_ext	NIMQChatSystemNotification
channel_id	NIMQChatSystemNotification
env	NIMQChatSystemNotification
from_accid	NIMQChatSystemNotification
from_client_type	NIMQChatSystemNotification
from_device_id	NIMQChatSystemNotification
from_nick	NIMQChatSystemNotification
history_enable	NIMQChatSystemNotification
msg_attach	NIMQChatSystemNotification
msg_body	NIMQChatSystemNotification
msg_data	NIMQChatSystemNotification
msg_ext	NIMQChatSystemNotification
msg_id	NIMQChatSystemNotification
msg_server_id	NIMQChatSystemNotification
msg_type	NIMQChatSystemNotification
need_badge	NIMQChatSystemNotification
need_push_nick	NIMQChatSystemNotification
push_content	NIMQChatSystemNotification
push_enable	NIMQChatSystemNotification
push_payload	NIMQChatSystemNotification
resend_flag	NIMQChatSystemNotification
route_enable	NIMQChatSystemNotification
server_id	NIMQChatSystemNotification
status	NIMQChatSystemNotification
timestamp	NIMQChatSystemNotification
to_accids	NIMQChatSystemNotification
to_type	NIMQChatSystemNotification
update_timestamp	NIMQChatSystemNotification