Added a brake controller which maps brake resistance and virtual speed
via a polynomial fit obtained from observations of the head unit.
Resistance is now set at sub-second intervals to ensure most recent
update is available for sending the brake.
Added some comments and cleaned up some magic numbers
Gradient Corrected Distance in course tracker
Refactored head unit and brake models into a shared model
Fixed typo
Fixed refactoring errors
Settings now cleared when no stored values are found
Merge branch 'powermodel' into unstable