Add helper to scan two sided in two scans

[Robert Ancell]

A common use case for a document feeder is to use a single sided scanner and scan the stack of pages twice.

i.e. 5 sheets of paper are sent through the document feeder twice, once for the front and once for the back.
In simple scan this leads to 10 pages in the document (F0F1F2F3F4B0B1B2B3B4 F=front, B=back). This needs to be manually reordered to make F0B0F1B1F2B2F3B3F4B4 using the "<" and ">" keys - does not scale to large documents.

There should be a feature to make this "simple".

[Robert Ancell (robert-ancell)]

Some options:
 * A Scan>Scan Backs option that does an ADF scan but inserts the B pages in the correct order.
 * Another "Scan Side" preferences - "Front and Back (two step)". In this case when the last page is scanned the user is prompted to reinsert the pages upside down and continue. The pages are correctly stitched together. This may be less discoverable than the first option. Putting a link to the preferences in the scan dropdown could solve this?