Minor Page List fixes

The list controller is no longer added to the window controller list
of the document, since this caused the list to randomly appear.
Current-Page detection

The current page is now detected by checking the distance of all
pages to the focus point instead of just checking vertical distance
to the anchor. This works properly with two side-by-side pages and
zoomed-in views.
New Geometry Helper functions for calculating distances between rects
and points are in CBGeometryHelpers.h.
CaseInsensitive Sorting

The sorting of pages after loading and during archive loading is now
case-insensitive.