Shutdown ESCs when IDLE

[olliewalsh]

Align IMU accelerometer axes. Calculate pitch, roll, and overall tilt angles.

Set ESC shutdown pin to HIGH if:

• not on a slope (pitch < 15deg) and...
• ROS is running and...
• current mode is IDLE

Requires killswitch to be set to ADC2_HIGH in xesc app config

(Based on the work of @Pete_MI632 on discord)