Adds Valkyrie-compatible Fixity Check service and a FileSet button to kick it off.

[bwatson78]

• app/controllers/hyrax/fixity_checks_controller.rb: overrides this Hyrax controller to make it call our custom service.
• app/jobs/fixity_check_job.rb: mirrors our Curate override of the same Job, but makes it Fedora v6/Valkyrie compliant.
• app/services/self_deposit/file_set_fixity_check_service.rb and app/services/self_deposit/valkyrie_fixity_service.rb: creates Valkyrie compliant services that are aware of the calling user.
• app/views/hyrax/file_sets/_show_details.html.erb: adds the requested button to kick off a fixity check.
• config/initializers/hyrax.rb: stubs our custom Fixity Service as the application configured choice.
• spec*: tests the new services and job.

[codeclimate[bot]]

Code Climate has analyzed commit afa420c2 and detected 0 issues on this pull request.

The test coverage on the diff in this pull request is 89.8% (50% is the threshold).

This pull request will bring the total coverage in the repository to 73.9% (1.2% change).

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