Adds an argument for setting a book's display name instead of title #13

src/main/resources/strings.yml

@@ -27,6 +27,7 @@ en:
   SUCCESS_GENERATION_CHANGED: "Book generation successfully changed!"
   SUCCESS_LORE_SET: "Added lore to item!"
   SUCCESS_TITLE_SET: "Title set to {title}!"
+  SUCCESS_DISPLAY_NAME_SET: "Display name set to {displayName}!"
   SUCCESS_MIGRATED: "Successfully migrated all books"
   SUCCESS_ENCRYPTED: "Book encrypted!"
   SUCCESS_UNSIGNED: "Book un-signed"