Added support for optional flat-list display of "All Books"

Files modified:

config_default.php

base.php

changed class PageAllBooks to test for configuration option "cops_titles_split_first_letter".
Used getCurrentOption to prepare for making Split Letter options configurable in web GUI

book.php

added SQL_BOOKS_ALL query to have a flat-list datasource not grouped by first letter.
added const SQL_BOOKS_ALL to class Book
added public static function "getBooks", called from Base::PageAllBooks to retrieve the flat-list