added background music and improved model code

reduced switch case for creating different ship models
created a new class for background music
added a button to toggle background music
added a slider so adjust volume
added new style for labeling the slider

Projekte/battleship/model/src/main/resources/battleship.properties

@@ -37,3 +37,7 @@ dialog.error=Error
 dialog.question=Question
 port.must.be.integer=Port must be an integer number
 map.doesnt.fit=The map doesn't fit to this game
+ships.dont.fit.the.map=Ships are out of bounds
+menu.music.toggle= Music on/off
+menu.music.volume= Volume
+