Working FS delete for /Image specs

This has only been tested with single-file image formats
(and not plates) but should allow clients to begin trying
to delete via the /Image spec (which is how the currently
delete)

The recursive nature of the fileset graph makes this more
complicated that would have otherwise been necessary. If
adding /Plate support is equally difficult, it may be necessary
to change how the Spring initialization works in order to
even circular dependencies.