In the Level Editor, the "Level->Attached files" menu opens the
FileSystem Window, which shows a paginated list of attached files and a
"Delete" button to remove them.
- Custom doodads which also exist locally can be deleted from the
level's filesystem at any time.
- If a custom doodad does NOT exist locally, and one of them is still
placed somewhere within the level, you can not delete it.
- You can't delete the custom wallpaper image IF the level is still
using it. Change to a default wallpaper and then you can delete the
custom wallpaper image.
