Storage - Added migration for plugin features

UI - Fixed an error on layer creation when the default brush is disabled

src/Artemis.Core/Services/Registration/Interfaces/ILayerBrushService.cs

@@ -26,6 +26,6 @@ namespace Artemis.Core.Services
         /// <summary>
         /// Returns the descriptor of the default layer brush
         /// </summary>
-        LayerBrushDescriptor GetDefaultLayerBrush();
+        LayerBrushDescriptor? GetDefaultLayerBrush();
     }
 }