"Scan side" with easier access in the main UI

[Jehan]

My scanner has double side feature. And I very regularly have one type or the other of documents so I always have to go to "Preferences", check the "Scan Side" option and very often I need update it (either "Front" or "Front and Back". The "Back" option is quite useless to me. I think I never used it). Even if I don't need to update it, I still go and check because I don't necessarily remember which option I used last.

I propose that this option be pushed into the main UI. For instance it could be a GtkSwitch next to the scan button. Or if we absolutely want to present the 3 options (with "Back"), it could be radio buttons, a combo menu or whatever you see fit. But I believe it should be visible from the main UI and switchable easily in a simple click without having to go in the preferences.