Port over remaining Point3D usage to the more type and unit safe SG* classes.

Port over remaining Point3D usage to the more type and unit safe SG* classes.
Remove leftover headers from plib/sg.

Modified Files:
 	src/AIModel/AIBase.cxx
 	src/AIModel/AIFlightPlanCreateCruise.cxx
 	src/ATCDCL/AIEntity.cxx src/ATCDCL/AIEntity.hxx
 	src/ATCDCL/AIGAVFRTraffic.cxx src/ATCDCL/AIGAVFRTraffic.hxx
 	src/ATCDCL/AILocalTraffic.cxx src/ATCDCL/AILocalTraffic.hxx
 	src/ATCDCL/AIMgr.cxx src/ATCDCL/ATC.hxx
 	src/ATCDCL/ATCDialog.cxx src/ATCDCL/ATCProjection.cxx
 	src/ATCDCL/ATCProjection.hxx src/ATCDCL/ATCutils.cxx
 	src/ATCDCL/ATCutils.hxx src/ATCDCL/approach.cxx
 	src/ATCDCL/commlist.cxx src/ATCDCL/ground.cxx
	src/ATCDCL/ground.hxx src/ATCDCL/tower.cxx
 	src/ATCDCL/tower.hxx src/Airports/calc_loc.cxx
 	src/Airports/dynamics.cxx src/Airports/groundnetwork.cxx
 	src/Airports/parking.cxx src/Airports/runwayprefs.cxx
 	src/Airports/simple.cxx src/Cockpit/cockpit.cxx
 	src/Cockpit/hud.hxx src/Cockpit/hud_card.cxx
 	src/Cockpit/hud_rwy.cxx src/Environment/environment.cxx
 	src/FDM/UFO.cxx src/FDM/SP/MagicCarpet.cxx src/GUI/dialog.hxx
 	src/Instrumentation/HUD/HUD.hxx
 	src/Instrumentation/HUD/HUD_runway.cxx
 	src/Instrumentation/KLN89/kln89.cxx src/Main/fg_init.cxx
 	src/Main/viewer.cxx src/Main/viewmgr.cxx
 	src/Model/panelnode.cxx src/MultiPlayer/mpmessages.hxx
 	src/Scenery/tilemgr.cxx src/Traffic/SchedFlight.cxx
 	src/Traffic/TrafficMgr.cxx