Update groundcache api:

Update groundcache api:
Make leaner interfaces to the groundcache.
Remove legacy interfaces.
Update users of them.
Add new query routines for 'nearest point' and 'body with given id'.

Modified Files:
	src/FDM/flight.cxx src/FDM/flight.hxx src/FDM/groundcache.cxx
	src/FDM/groundcache.hxx src/FDM/JSBSim/JSBSim.cxx
	src/FDM/JSBSim/JSBSim.hxx src/FDM/YASim/FGGround.cpp
	src/FDM/YASim/FGGround.hpp src/FDM/YASim/Gear.cpp
	src/FDM/YASim/Gear.hpp src/FDM/YASim/Ground.cpp
	src/FDM/YASim/Ground.hpp src/FDM/YASim/Model.cpp