Handle tile/image requests for non-image sources

[donaldgray]

The different families of asset, (I)mage, (T)imebased and (F)ile are all called on differently prefixed paths (/iiif-img/, /iiif-av/ and /file/ respectively).

The slug should represent the output rather than the underlying family.

Cantaloupe supports frame extraction from video files and page extraction from PDFs via meta-identifiers.

• identifier
• identifier;page_number
• identifier;scale_constraint
• identifier;page_number;scale_constraint

Handle T and F assets on /iiif-img/ path. We will need to:

• check the family of the requested asset.
• if family=I, process as-is. else,
• if family=F, process like image (optionally check if PDF)
• if family=T, hand off to Cantaloupe. The exact logic will depend on Cantaloupes handling - ideally it can extract a frame without copying the entire file to local disk.

[tomcrane]

This issue needs rewriting for Delivery Channels