Rework Dual pages code so that the view is considered
a single page number, so it looks more like 2-columns
on a single page.
This solves a few issues like:
- Page number and count are consistent between top
and bottom status bars
- SkimTo -1/+1 doing nothing every other tap
- Statistics being wrong (like "Pages read" never
going over half of the book page count)
05126b94b6