Allows you to put hollowed-out books in bookcases

Fixes #6668
it's sad that this is how this has to be done, However:

replace those 3 (4 with tk's) typepaths with a list containing those typepaths, and just run is_type_in_list() on the list. call it allowed_books or something.

```
var/list/allowed_books = list(/obj/item/weapon/book, /obj/item/weapon/spellbook, etc.)
if(is_type_in_list(I, allowed_books))
    do_stuff()
```