Move title specification for settings groups to constructor

Using an abstract property was awkward for this as it is being consumed
in the underlying constructor but could not be dynamically set in time from a
derived class.

osu.Game.Tests/Visual/Gameplay/TestSceneReplaySettingsOverlay.cs

@@ -48,7 +48,10 @@ namespace osu.Game.Tests.Visual.Gameplay
 
         private class ExampleContainer : PlayerSettingsGroup
         {
-            protected override string Title => @"example";
+            public ExampleContainer()
+                : base("example")
+            {
+            }
         }
     }
 }