Aligning TuyaMCU code with Tasmota naming conventions

[blakadder]

Description:

Building on top of shantur's PR I changed:

• TuyaMCUReceived to TuyaReceived to keep with established naming scheme (SerialSend/SerialReceived; TuyaSend/TuyaReceived)
• Changed topic of TuyaReceived from tele/%topic%/RESULT to stat/%topic%/RESULT

Checklist:

• The pull request is done against the latest dev branch
• Only relevant files were touched
• Only one feature/fix was added per PR.
• The code change is tested and works on core pre-2.6
• The code change pass travis tests. Your PR cannot be merged unless tests pass
• I accept the CLA.

[shantur]

@blakadder : You might want to align the topic with SerialReceived and SSerialReceived. They both use tele not stat.

https://github.com/arendst/Sonoff-Tasmota/blob/development/sonoff/sonoff.ino#L1250
https://github.com/arendst/Sonoff-Tasmota/blob/development/sonoff/xdrv_08_serial_bridge.ino#L76

@ascillato2

[arendst]

You're right. I will adjust.