The FileImporter will try to change templates based on the CommonsHelper2's config files. Right now, users wouldn't be able to see a diff of what changed until after they did the import.
- Add a "Show changes" button next to the import link on the preview page, in accordance of how it usually looks on article pages, see screenshot
- When the button is clicked, show a diff between what the file info was before the import, and now. Remember that this is the no-js version. The diff should also have a button "back to preview"