Introduce example for a more flexible deserialization

Also make the CoverGenerator themes serializeable
Rest is automatic reformatting.

VocaluxeLib/Menu/CMenu.cs

@@ -25,6 +25,7 @@ using System.Xml.Serialization;
 using VocaluxeLib.Draw;
 using VocaluxeLib.Menu.SingNotes;
 using VocaluxeLib.Menu.SongMenu;
+using VocaluxeLib.Xml;
 
 namespace VocaluxeLib.Menu
 {