Revert "Remove all references to DigestUtils, replace with references to new MD5 code"

This reverts commit d97d5e6e7866c5ec0d31cf2dd982f1cd1ad163bd.
Revert "Added MD5 library for testing alternative implementation"

This reverts commit df5d9e25af29f625b2648815153e4f3add0a0ba4.