ENH: Added all ITK images to the manifest for downloading.

cd ITK

for i in $(find . -name "*.md5"); do \
      echo -e \
      "[\n\"ITK/${i//.md5/}\",\n\"$(cat $i)\"\n],"; \
done \
> SimpleITK-Notebook-Answers/Data/ITK_manifest.json

cd SimpleITK-Notebook-Answers/Data
python ../SimpleITK-Notebooks/Data/mergejson.py manifest.json
ENH: merged features and add fdata for all downloads
ENH: Renamed to remove filename spaces.
Merge pull request #4 from hjmjohnson/AddExternalDataUpdateSITKCalls

Add external data update sitk calls
ENH: Pushed items into common location for re-use.