Add 'speed limit' shell function.

Add a new 'speed limit' function that sets the reference speed as in
done in 'speed' with arg1. After the bike has travelled distance arg2,
specified in meters, reference speed is changed to 1.0 m/s.
Do not reset integrator state when changing speed.
Change steer, lean LED logic depending on bike state.

LED logic is dependent on current bike state: STARTUP, COLLECT, RUNNING,
RAMPDOWN. Add an optional field to Sample.proto which is used to track
the bike state and the field is not written to file.
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.