Editor should not lose track of file when dragged to file system

1. Open a file in Creator.
2. From there, drag and drop the file into a file manager.
   The file will be moved to the location where you dropped it.
3. Go back to Creator.
   Creator will complain that the file was removed.

Instead, the editor should keep working with the new location of the file. This might be tricky when the file is part of a project, so maybe it's safer to disable dragging files from editors to the file system completely.