Add settings for number of books/shelves that will be displayed per page

[Xenoamor]

A trivial addition to allow setting the number of paginated results on the books/shelves tab. Unfortunately I could not find a way to do this using the Logical Theme System

I'm not sure if these settings would be better placed under the "Customization" tab but I have placed them under "Sorting" for the moment. Unfortunately this does require 4 new strings in the localization files

This would close #2343