PDF view: Allow two/double pages view

Like here:

This would really help e.g. using seafile like a book/ pdf libary in the browser (no extra downloads).

Edit: Translation: “Single page”, “odd + even page” (maybe also called double page), “even + odd page” (maybe also called book view, because a books content starts with 2 as 1 is the cover page).

Thanks for the feedback. We will record the feature request.