changed migrationhandler to support property name change, also added setting of dirty flag - else serialization stomps over our code change

Author: bethalha-havok

Assets/MixedRealityToolkit.SDK/Experimental/Features/Utilities/Migration/BoundsControlMigrationHandler.cs

@@ -288,10 +288,11 @@ private void MigrateAppBar(BoundingBox boundingBox, BoundsControl boundsControl)
             for (int i = 0; i < appBars.Length; ++i)
             {
                 AppBar appBar = appBars[i];
-                if (appBar.BoundingBox == boundingBox)
+                if (appBar.Target == boundingBox)
                 {
                     Undo.RecordObject(appBar, "BoundsControl migration: changed target of app bar.");
-                    appBar.BoundingBox = boundsControl;
+                    appBar.Target = boundsControl;
+                    EditorUtility.SetDirty(appBar);
                 }
             }
         }