libview: Keep the scrollbar position when navigating

Maintain the position of the scrollbar to maintain the text position
while navigating from one page to another.

The issue occurs when the visual area is smaller than the actual page.

Closes #16

https://bugzilla.gnome.org/show_bug.cgi?id=318337
5 jobs for issue-16-keep-scrollbar-position in 5 minutes and 22 seconds (queued for 3 seconds)
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