2up: better initial sizing of page view area (books with small title page and wide interior pages)

When arriving at the BookReader in 2up we size the view area to fit that page. For books where this page is small and the other pages are small, the subsequent experience is not good since the book will spill outside the view area. We could autodetect this possibility and make the initial view sized to fit the "normal" pages of the book.

e.g. for these micro-films the de facto title page is small and the subsequent pages are wide:
http://www-testflip.archive.org/stream/newyorkcensus00reel1526#page/n0/mode/2up