Introduce example for a more flexible deserialization

Also make the CoverGenerator themes serializeable
Rest is automatic reformatting.

VocaluxeLib/Menu/CSelectSlide.cs

@@ -20,6 +20,7 @@ using System.Collections.Generic;
 using System.Drawing;
 using System.Xml.Serialization;
 using VocaluxeLib.Draw;
+using VocaluxeLib.Xml;
 
 namespace VocaluxeLib.Menu
 {