The `StopRinging()` function was used just in `Notifications.h` screen.
That screen already has access to a `motorController` object.

Don't use relative imports like `../foo.h` as those depend on the
relative position of both files. Rather than that use imports relative
to the `src` directory, which explicitly is part of the include
directories.

Remove the unused include `app_timer.h` in `MotorController.h`