[MSE::Delete] Trying to load a scene which was deleted throws exception, should show pop-up "cannot load deleted scene

Steps to repro:
1. Open the attached project
2. Unlaod the scene 2 from the hierarchy view
3. Delete scene 2 from assets
4. Now try to load scene 2 from hierarchy view

Note that an exception is thrown. The exception thrown is not incorrect but it should be handled in a different way.
1. One option is to delete the unloaded scene entry from the hierarchy view as well when we delete from assets folder
2. Show a pop up which says it cannot be loaded and ask user for confirmation to remove it from the hierarchy view