Make use of more available space in page range selection

The dialog for selecting a start page (and in the near future, a page range) from a book doesn't make use of all available space, which means a lot of scrolling is required. This dialog would be easier to use if it was sized to make use of more of the available space and/or could be resized by the user.

Example showing unused space:

Note that this screenshot includes some new elements (page range controls at bottom, visual display of hierarchy) which are not yet present in the main branch.