Simplify hvac main.cpp code

Close for GG RC2

Hello @knimitz 

I shall create a ticket for the same.

Thanks

Discussed with Scott and Jan-Simon. No cherry pick to Flounder desired. 

This work finished.

@supriya sirbi , if you will address simplifying other applications, please create new ticket.

Hello, @supriya sirbi, thank you for your suggestion.

Unfortunately, I have done the work for hvac. But for other application such like dashboard, mixer and so on, I didn't apply qtaglextra to simplify those main.cpp because those applications use QUrl(bindingAdress) from arguments. qtaglextras creates the same object internally and export to QML so QML can use it.

I would like to find the solution.. but I don't have... Can you simplify those applications ?