COMP: C++11 style nullptr usage

Use clange-modernize to identify and replace NULL and 0 with nullptr.

This is good practice to ensure that pointers are properly managed.

clang-modernize -p BRAINSTools-build/ -include BRAINSTools -use-nullptr
COMP: Use C++11 keyword override for code maintenance

clang-modernize -p BRAINSTools-build/ -include BRAINSTools -use-nullptr
-add-override   -override-macros

Using the new C++11 keyword will help with future code maintenance.
COMP: Remove unused typedefs

To keep code clean, remove unused local typedefs

warning: unused typedef [-Wunused-local-typedef]
ENH: Updated VTK.
COMP: Improve VTK compilation options.
BUG: Changes to Fix 'space directions' field in the NRRD Header

Bug fixed and tested by Vincent A. Magnotta.