ENH: Add Utilities/Maintenance/ContentLinkSynchronization.sh
ENH: Add Utilities/Maintenance/ContentLinkSynchronization.sh

This script, given an ExternalData object store, checks all ExternalData
.md5 and .sha512 content links in the ITK source, verifies that hashes
correspond to the same file, and creates both .md5 and .sha512 hashes if
they are missing.

If content link verification fails, the script notifies the caller and exits.
The error should be resolved manually before re-execution.

Once executed, a commit can be created from the result.

This script should be executed prior to releases. After any missing content
links have been merged, the scripts to archive testing data on the Midas and
Girder stores should be executed.

Change-Id: Ib55da90139834093fd70881f983f9e51168c7ac0

stnava/ITK,malaterre/ITK,InsightSoftwareConsortium/ITK,spinicist/ITK,vfonov/ITK,thewtex/ITK,blowekamp/ITK,malaterre/ITK,PlutoniumHeart/ITK,hjmjohnson/ITK,InsightSoftwareConsortium/ITK,BRAINSia/ITK,LucasGandel/ITK,Kitware/ITK,Kitware/ITK,spinicist/ITK,spinicist/ITK,stnava/ITK,thewtex/ITK,InsightSoftwareConsortium/ITK,vfonov/ITK,stnava/ITK,PlutoniumHeart/ITK,richardbeare/ITK,InsightSoftwareConsortium/ITK,thewtex/ITK,PlutoniumHeart/ITK,fbudin69500/ITK,BRAINSia/ITK,PlutoniumHeart/ITK,LucasGandel/ITK,InsightSoftwareConsortium/ITK,thewtex/ITK,thewtex/ITK,vfonov/ITK,malaterre/ITK,vfonov/ITK,spinicist/ITK,LucasGandel/ITK,fbudin69500/ITK,spinicist/ITK,InsightSoftwareConsortium/ITK,spinicist/ITK,spinicist/ITK,hjmjohnson/ITK,spinicist/ITK,hjmjohnson/ITK,richardbeare/ITK,stnava/ITK,hjmjohnson/ITK,vfonov/ITK,richardbeare/ITK,malaterre/ITK,fbudin69500/ITK,blowekamp/ITK,stnava/ITK,BRAINSia/ITK,Kitware/ITK,vfonov/ITK,blowekamp/ITK,fbudin69500/ITK,BRAINSia/ITK,Kitware/ITK,stnava/ITK,vfonov/ITK,Kitware/ITK,LucasGandel/ITK,blowekamp/ITK,blowekamp/ITK,hjmjohnson/ITK,PlutoniumHeart/ITK,richardbeare/ITK,vfonov/ITK,InsightSoftwareConsortium/ITK,BRAINSia/ITK,LucasGandel/ITK,thewtex/ITK,thewtex/ITK,malaterre/ITK,malaterre/ITK,blowekamp/ITK,fbudin69500/ITK,hjmjohnson/ITK,blowekamp/ITK,BRAINSia/ITK,stnava/ITK,BRAINSia/ITK,malaterre/ITK,LucasGandel/ITK,LucasGandel/ITK,richardbeare/ITK,fbudin69500/ITK,richardbeare/ITK,blowekamp/ITK,richardbeare/ITK,spinicist/ITK,malaterre/ITK,Kitware/ITK,fbudin69500/ITK,fbudin69500/ITK,vfonov/ITK,stnava/ITK,hjmjohnson/ITK,malaterre/ITK,LucasGandel/ITK,PlutoniumHeart/ITK,PlutoniumHeart/ITK,stnava/ITK,PlutoniumHeart/ITK,Kitware/ITK