[RIP-11]MQTT:completing pub and sub logic of qos=0 messages(single node only )

[xiangwangcheng]

What is the purpose of the change

finish single-node version of publish and subscribe logic of qos=0 messages

Brief changelog

1. completing logic of publishing and subscribing, unsubscribing
2. polish the logic of encode/decode between MqttMessage and RemotingCommand
3. add some NPE inSnodeController.java

Verifying this change

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[duhenglucky]

Very glad to see that have already completed the pub/sub logic in qos0 level, but there are still exists some issues about this PR， and we also need to add more unit test in this module, and in the later, IMO, we should separate the mqtt related codes to a single module.

[duhenglucky]

Maybe we can define a mqttConfig class to manage these configs related to MQTT.

[duhenglucky]

Please don't change the code format if we have no change about this, it will lead us difficult to review these codes later

[duhenglucky]

why do you want to add a new property here? and it would be nice if we can use byte[] body instead.

[zongtanghu]

Please rebase and resolve the conflict codes in the Conflicting file list.