COMP: Add c++11 flags for maintenance

Adding flags that can assist with maintenance over
time by using features in c++11.

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

C++11 provides the override keyword to assit with identifing
functions that are meant to be override the base class
implementation.  This refactoring adds the override keyword
in order to enhance compile time identification of
errors that may be introduced during refactoring.

The following substitutions were heavily used during
the code instrumentation of the override keyword:

:s/)$/) ITK_OVERRIDE/ge
:s/);$/) ITK_OVERRIDE;/ge
:s/) *const *;$/) const ITK_OVERRIDE;/ge
:s/const *{/const ITK_OVERRIDE {/ge
:s/) *const$/) const ITK_OVERRIDE/ge
:s/() *{}$/() ITK_OVERRIDE {}/ge
:s/) = 0;$/) ITK_OVERRIDE = 0;/ge
:s/) *const *= *0;$/) const ITK_OVERRIDE = 0;/ge
:s#();  *//#() ITK_OVERRIDE;  //#ge
STYLE: Remove unused typedefs

Removed typedefs that were not necessary.  This helps
to keep the code clean and easier to maintain.
Merge pull request #140 from stnava/CodeMaintenanceStyle

Code maintenance style