Fixes and improves book saving

Removes redundancy
Fixes broken duplicate checking
Moves the save function to its own class

src/main/resources/plugin.yml

@@ -53,6 +53,10 @@ commands:
     description: Saves the held book to the public books folder
     usage: /<command> [duplicate (true/false)]
     permission: bookswithoutborders.savepublic
+  save:
+    description: Saves the held book to the holding player's folder
+    usage: /<command>
+    permission: bookswithoutborders.save
 permissions:
   bookswithoutborders.admin:
     description: Grants all permissions