This commit adds the VTK_USE_CXX11_FEATURES variable for newer versions
of CMake (>=3.3).  This turns on target_compile_features for override,
final and nullptr on vtkCommonCore and adds a detection header to create
macros for these for use throughout VTK.  VTK_OVERRIDE, VTK_NULLPTR and
VTK_FINAL can now be used.  This new header is included in
vtkConfigure.h so these should be available everywhere.