Use Stock Hyrax Thumbnail Derivative for IIIF Manifest

[joncameron]

Descriptive summary

Within hyrax-iiif_av, we could continue using the same image for both thumbnail and posterCanvas attributes in the IIIF manifest. Eventually we'll want to have different poster and thumbnail images coming from active_encode, but we already have the stock hyrax thumbnails so we can use them for first implementation.

Done Looks Like

• hyrax-iiif_av is updated to include the default Hyrax thumbnail for the thumbnail and posterCanvas images within the manifest

Related Item

• Use Stock Hyrax Thumbnail Derivative for IIIF Manifest avalon-bundle#276
• Implement posterCanvas for Presentation 3.0 samvera/iiif_manifest#33