Add support for IIIF requiredStatement on Cantus Ultimus

[dchiller]

From @ahankinson in a discussion at CantusDB#1072:

The IIIF manifests usually have a requiredStatement that are required, by the spec, to be shown by viewers. This usually specifies the institution that provides the images.

There is also a provider section that can give more information about the source of the manifest.

https://iiif.io/api/presentation/3.0/#requiredstatement

IIIF v2 had attribution and logo sections.

We need to add support for these required statements so Cantus Ultimus is in compliance with IIIF standards.

[annamorphism]

to be clear, does adding the requiredStatement in CU mean we no longer need to worry about whether CantusDB links to CU or to the original archive? or is it sort of a both/and situation?

[dchiller]

Both/and...

We need to add the requiredStatement because it turns out that IIIF viewers need to do that to be considered "up to code". And because it would generally good to provide credit where credit is due on images we are showing on Cantus Ultimus.

It seems to me based on the discussion in DDMAL/CantusDB#1072 that we still don't have a settled decision on when CantusDB links to where.

[annamorphism]

Ok, sounds like a discussion is in order then!

[dchiller]

Note: In the Presentation API v 2, the equivalent seems to be the attribution attribute.