INDENTATION
GreedySubFlightPlanner returns bool instead of void
Added SubFlightPlanner and DubinsSubFlightPlanner

SubFlightPlanner is the "master" planner for sub flights. Depending on
the directionality of the sensors it subcontracts with
GreedySubFlightPlanner or DubinsSubFlightPlanner.

DubinsSubFlightPlanner is for making sure that sensors with directional
sensors have the proper approach direction.
HierarchicalPlanner now uses the new SubFlightPlanner