Handle different image stack types

The image extraction code works with ( image format, archive format) types:

( jp2, zip )
( tif, zip )

... but others exist in Archive items. We need to add at least ( jp2, tar ) and ( jpg, single-file ) and preferably decouple image format handling from archive format handling.

Start by locating the image extraction code and the handling of Archive items. Trace how image and archive formats are currently paired, then add support for jp2 in tar archives and jpg as a single file; done means these image stack types are extracted correctly, with format handling decoupled if feasible.

Written by the indexing model from the issue text.