Miscellaneous tweaks and Bugfixes. Mostly memory leaks ported from the plib

Miscellaneous tweaks and Bugfixes. Mostly memory leaks ported from the plib
version
* Delete ai list objects in ~ATC/AIMgr.cxx:AIMgr::~AIMgr()
* Delete colors in GUI/new_gui.cxx: NewGui::~NewGui.cxx
* Delete memory allocated to the class member "route" in
  Instrumentation/gps.cxx
* Delete all globals (except a few "unsafe" ones that still cause segfaults
  and need further examination.
* Use an SGShared pointer for navaid memory allocation, so that pointers to
  individual navaid objects can be included safely in multiple navaid lists