exact duplicate pictures clean-up (hashes, merging, re-direct)

[puik]

We have instances of exact duplicate historic images – exactly the same picture (= image file) has been imported from some repositories several times (mostly from Muis.ee and Finna.fi).

• we need to add hash calculation to all files
• compare hashes (and source IDs or url)
• perform merging of duplicate pictures and also merge all the activity to the remaining picture
• have redirect from merged Ajapaik ID to the remaining