also direct throttle nudge replaced with speed nudge
calc_speed_max estimates vehicle's top speed based on cruise-speed and
cruise-throttle
steering mode now provides total target speed instead of using speed plug
throttle nudge
motor limits provided to attitude control to stop i-term buildup
uses negative desired speed instead of reversed flag
reporting to GCS uses new throttle controller
braking is simply enabled and allows a reverse motor output regardless of vehicle
speed
updating mission is handled by the vehicle code
slows down for turns
add active at destination
remove setting of loiter start time
removes unused calc_nav_steer
