Replace pixelsId by imageId to reduce number of calls.
Remove unused import.
No longer returned silently an OME-TIFF (see #8188)

Prepare the call so it is easier to merge to FS branch
Modify result handling of archived download

* if no archived, indicate to load as OME-TIFF
* if more than one image, create a zip.
Merge pull request #717 from jburel/download-original-file

Download original file