Fix static lean calculation.

Static lean calculation now uses accelerometer y instead of accelerometer x as
the imu signals are now given in the bicycle lean frame.
Merge remote-tracking branch 'oliverlee/setpoint' into imu_calibration
Add yaw rate PI controller.

This commit adds Matlab code for design of PI controller gains, output of yaw
rate measurement matrix, and firmware updates to implement PI yaw rate control.
No anti-windup is performed so we need to verify that steer torque does not
saturate. Crossover frequency was selected to be 0.1 Hz. Strangely, the Matlab
pidtune() function yields an integral only controller even though a PI
controller is requested.
Merge remote-tracking branch 'oliverlee/setpoint' into imu_calibration

Conflicts:
	firmware/src/control_loop-inl.h
Fix sign error on distance calculation.

Minor cleanup of illuminate_lean_steer() code.
Fix distance error, led toggling, yaw rate LED threshold.
Add sinusoidal disturbance command.

Set a sinusoidal disturbance to add to the control torque, which takes
two args, the amplitude and the frequency. Amplitude is in N-m,
frequency is in Hz. Disturbance will be enabled after the bike state
norm is less than 0.5.