Allow users to download individual high-res files

[helrond]

Is your feature request related to a problem? Please describe.

Users sometimes want hi-res copies of individual images that are published on DIMES. Right now they have to request these from archivists, which requires a lot of unnecessary intervention and work.

Describe the solution you'd like

Allow users to download individual hi-res JPEG 2000 files directly from S3. This would be done in Mirador, so that a specific page could be targeted, and would require the existing button to be converted to a dropdown with options to download a single image or a PDF of all images.