Improve diff visualization for non-text fields

- [ ] `date` should be displayed in user locale instead of ISO date
- [ ] `multiselect` and `option` should display the localized text instead of the technical key
- [ ] `multiselect` and `option` diffs could be more granular; compare the label as a whole instead of individual letters
- [ ] `multiselect` could be visualized as a list instead of comma-separated text
- [x] `attachment` is currently comparing file names; it should check if file content has changed and offer links to the old and new versions