Fixed some Errors with Books

Now verses aren't cut off between pages.

How often you get a notification of chapters being finished can be
configured.

Parts of verses don't go missing from books.

NullPointerExceptions were fixed.

Typos were fixed in the CheckBooks class.

igBooks(in game books)'s configs are now named
<translation>bookconfig.yml instead of <translation>config.yml.

Simplified MainCommandExecutor.