motion commander, start_linear_motion reverse yaw

[knmcguire]

If somebody uses the start_linear_motion function from the motioncommander, and add a yaw_rate, you'll see that the resulting yaw rate on the crazyflie itself is reversed, compared to the coordinate system that we have given in our documentation: https://www.bitcraze.io/documentation/system/platform/cf2-coordinate-system/

This was originally introduced with this PR: bitcraze/crazyflie-firmware#338 and implemented in all packets there forth. The problem is that the coordinate system is consistent with the state estimate but not consistent with the control input...

[knmcguire]

Also related a bit to this bigger picture conversation of the crazyflie-firmware: bitcraze/crazyflie-firmware#396

[knmcguire]

this needs to be investigated as it is being negated in multiple places, and eventually again in the firmware...