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

	antiSpamOption	NIMCustomSystemNotification
	apnsContent	NIMCustomSystemNotification
	apnsPayload	NIMCustomSystemNotification
	content	NIMCustomSystemNotification
	env	NIMCustomSystemNotification
-	initWithContent:	NIMCustomSystemNotification
	notificationId	NIMCustomSystemNotification
	receiver	NIMCustomSystemNotification
	receiverType	NIMCustomSystemNotification
	sender	NIMCustomSystemNotification
	sendToOnlineUsersOnly	NIMCustomSystemNotification
	setting	NIMCustomSystemNotification
	timestamp	NIMCustomSystemNotification