Expose API for giving and taking experience levels for use with ExpCommand's new behaviour with Minecraft 1.4. Adds BUKKIT-2739

By: EvilSeph <evilseph@gmail.com>

paper-server/src/main/java/org/bukkit/craftbukkit/entity/CraftPlayer.java

@@ -539,6 +539,10 @@ public class CraftPlayer extends CraftHumanEntity implements Player {
         getHandle().giveExp(exp);
     }
 
+    public void giveExpLevels(int levels) {
+        getHandle().levelDown(levels);
+    }
+
     public float getExp() {
         return getHandle().exp;
     }