Accel calibration wizard fix

This fixes the attitude image for accelerometer calibration. The calibration messages in the firmware changed [here](https://github.com/PX4/Firmware/commit/b51c6693445be6ff230b3d34ad400553aadddd7e#diff-90fdbb318fd7b63a58510762a295f790), so QGC needs to parse them differently.

To work consistently, this needs an update on the firmware side as well (PR on the way). I assumed the direction it outputs is always the one facing downwards.

The current approach here is a bit hacky (parsing the messages)... Since the calibration logic itself is able to determine the current position anyway, maybe the better option would be to just add an image that shows every position and tell the user go through each of them. Thoughts?