Fixes and improves book saving

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

src/test/java/net/knarcraft/bookswithoutborders/util/FileHelperTest.java

@@ -0,0 +1,25 @@
+package net.knarcraft.bookswithoutborders.util;
+
+import net.knarcraft.bookswithoutborders.utility.FileHelper;
+import org.junit.Test;
+
+import java.io.File;
+
+import static org.junit.Assert.assertEquals;
+
+public class FileHelperTest {
+
+    @Test
+    public void findDuplicatesTest() {
+        File[] files = new File[5];
+        files[0] = new File("test/asd/book+)Fish.yml");
+        files[1] = new File("test/asd/book+)Crab.yml");
+        files[2] = new File("test/asd/(3)book+)Crab.yml");
+        files[3] = new File("test/asd/(2)book+)Crab.yml");
+        files[4] = new File("test/asd/(1)book+)Crab.yml");
+        assertEquals(4, FileHelper.findDuplicates(files, "book+)Crab.yml"));
+        assertEquals(1, FileHelper.findDuplicates(files, "book+)Fish.yml"));
+        assertEquals(0, FileHelper.findDuplicates(files, "book+)Horse.yml"));
+    }
+
+}