fix coredump at exit about qtodotxt2

[fuchsmich]

I will try to move all the setup stuff (args, singleton,...) from app.py to main_controller.py.
Then we can export the MainController to qml as a class to qml, it gets instanciated there and also dies properly with the exit of the application.

Maybe this solves this issue.

[oroulet]

I would prefere not to have the singleton and arg stuff into MainController class... wait a little with that one.

[oroulet]

done. Looks like qml stuff needed an explicit aprent