Moves the save public command to its own class

src/main/resources/plugin.yml

@@ -49,6 +49,10 @@ commands:
     description: Sets the lore of the held item
     usage: /<command> <new lore>
     permission: bookswithoutborders.setlore
+  savepublic:
+    description: Saves the held book to the public books folder
+    usage: /<command> [duplicate (true/false)]
+    permission: bookswithoutborders.savepublic
 permissions:
   bookswithoutborders.admin:
     description: Grants all permissions