Solution for Nr. 10, added 'BackgroundSound.java' and edited 'battleshipApp' and 'Menu'

the 'BackgroundMusic' class defines the background music and the function used to control it, in the 'BattleshipApp' is an attribute of BackgrounMusic and a return function and in the Menu the Checkbox and the slider for the backgroundMusic and the update function were implemented

Projekte/battleship/model/src/main/java/pp/battleship/notification/Sound.java

@@ -22,10 +22,5 @@ public enum Sound {
     /**
      * Sound of a ship being destroyed.
      */
-    DESTROYED_SHIP,
-
-    /**
-     *
-     */
-    BACKGROUND_MUSIC //TODO
+    DESTROYED_SHIP
 }