Use M3 instead of OSD for uploaded items

[camillevilla]

Split out from #1415, info in forthcoming ticket

[camillevilla]

Will require a new Spotlight release post projectblacklight/spotlight#2217, else:

Blocked loading mixed active content “http://exhibits-stage.stanford.edu/images/4175/info.json”iiif:1:875

After we upgrade to Spotlight v2.11.0, we should see a CORB error instead.

[camillevilla]

We currently avoid the headache of building Mirador 3 in exhibits by serving up an iframe via our oEmbed service.

Curators won't be able to view the images they uploaded until they publish their exhibits. We decided to split this from #1415 after discussing the potential support burden with @caaster.

I'm not sure we have the bandwidth to fix this before our next work cycle begins, so I just wanted to document our current understanding of the problem.

Published exhibit

Private exhibit

Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource 
at https://exhibits-stage.stanford.edu/external-iiif-and-upload-images-test-august-
2019/catalog/107-6912/manifest. (Reason: CORS header ‘Access-Control-Allow-Origin’ missing).


Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource
 at https://exhibits-stage.stanford.edu/external-iiif-and-upload-images-test-august-
2019/catalog/107-6912/manifest. (Reason: CORS request did not succeed).