Filehash Fixes and improve checksum view

[rosiel]

GitHub Issue: Islandora/documentation#1931

Islandora requires the filehash module, and provides (in the core features) settings(!!) and a view that use it.

Since the update to filehash 2, the view has been broken. (Filehash 2 stores data in fields on files, so the plugin handler was different)

Also! Filehash 2 provides some great features:

• store the "original" checksum of the file (on the creation of the file entity)
• re-hash the checksum any time the file changes.

Is it the be-all-and-end-all of preservation fixity for a repository? No! lol, but we can do a lot more with it now than we could before.

What does this Pull Request do?

Updates the settings and view to work with the new filehash module.

What's new?

• Turn on features to re-hash files when changed, and store the hash of the original.
• For the view that exposes checksums at /checksum/{file_id}, include the original hash, and lock it down so that you need 'View checksums' permission to see the view (That permission had been defined, but seemingly never used?)
• Does this change add any new dependencies? Changes dependencies - filehash 2.
• Does this change require any other modifications to be made to the repository
  (i.e. Regeneration activity, etc.)? Upgrade will involve regenerating filehashes.
• Could this change impact execution of existing code? I can't tell if the view's contents are used anywhere. Even if they are, I added an additional element and left what was in place.

How should this be tested?

Load the starter site. (or try to update filehash to 2.x on the install profile?)
Go to the View "File checksums" and see it's missing a handler.
Load this PR.
Go to the Islandora Core Feature, in Features.
Select views.view.file_checksum and filehash.settings, and import the changes.
Create some test files.
Go to the View. It should not be broken. Test at /checksums/1 (replace 1 with your file id) and see a JSON array containing checksums, including 'sha1andoriginal_sha1`

Note: Derivatives will have empty original_sha1. The derivative code creates the file empty, then updates it with the content.

Documentation Status

• Does this change existing behaviour that's currently documented? lol, not documented
• Does this change require new pages or sections of documentation? yeah, maybe
• Who does this need to be documented for? site builders
• Associated documentation pull request(s): ___ or documentation issue ___

Additional Notes:

Any additional information that you think would be helpful when reviewing this
PR.

Interested parties

Tag (@ mention) interested parties or, if unsure, @Islandora/committers

[rosiel]

Found another thing to add to this.

• the new structure of filehash is causing our check in hook_update_file() to fail, meaning we create double derivatives.
• Filehash is failing during the derivative creation process, when we create a file object that has no actual file in it. we could maybe fix?

[rosiel]

OK, the latest commit 7df45a0 should fix the check in hook_file_update() and the double derivative thing.

there's kind of a larger issue here that we could use filehash more effectively/reliably but I think that's a separate issue

[nigelgbanks]

Reviewed and tested. Working as intended.