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)
Default setting set by holding on the bottom config buttons
for "View mode" (scroll/page) and "Progress bar" (full/mini)
were not used.
Also, when switching Progress bar from 'full' to 'mini',
show the mini bar again.