During package planning we don't care about the details of the flight
plan, just the layout (to check if the layout is threatened and we need
escorts). Splitting these will allow us to reduce the amount of work
that must be done in each loop of the planning phase, potentially
caching attempted flight plans between loops.
Split the oversized file into one per plan type. This also moves the
layout responsibility out of the oversized FlightPlanBuilder and into
each flight plan type file.
