ENH: add ITK_OVERRIDE when missing

Add ITK_OVERRIDE msotly in Monteverdi

save override in OTB (need to manually fix this after tidy)
  cd src/Modules ; grep -nR "override" * > ~/temporary/override_otb.txt
  cd ~/software
  python run-clang-tidy.py -checks=-*,modernize-use-override -header-filter=/home/grizonnetm/projets/otb/src/OTB/Modules/.*/.*/include/.* -j8 -fix -p ~/projets/otb/bin/release/OTB-clang3.8/ ~/projets/otb/src/OTB/Modules/*/*/src/*.cxx ~/projets/otb/src/OTB/Examples/*/*.cxx ~/projets/otb/src/OTB/Modules/*/*/test/*.cxx > ~/temporary/run-clang-tidy-log.txt
  #rename override with ITK macro ITK_OVERRIDE
  cd src/Modules
  find . -path ./ThirdParty -prune -o -type f -print -name "*.h" -o -name "*.txx" | xargs perl -pi -e 's/\ override/\ ITK_OVERRIDE/g'