Implement a common Interface for all MenuElements

Also remove CSongMenu and replace it with a factory class

PartyModes/PartyModeChallenge/CPartyScreenChallengeConfig.cs

@@ -144,12 +144,6 @@ namespace VocaluxeLib.PartyModes.Challenge
             return true;
         }
 
-        public override bool Draw()
-        {
-            base.Draw();
-            return true;
-        }
-
         private void _RebuildSlides()
         {
             // build num player slide (min player ... max player);