Use hash for external-data key
Use hash for external-data key

The external data was never being updated. Now we use the a check some
of the last commit message to the "Testing/Data" directory so that the
cache will be updated when the Testing data is updated.

kaspermarstal/SimpleElastix,kaspermarstal/SimpleElastix,kaspermarstal/SimpleElastix,kaspermarstal/SimpleElastix,kaspermarstal/SimpleElastix,kaspermarstal/SimpleElastix,kaspermarstal/SimpleElastix