Steps to reproduce:
- go to a File page e.g. https://commons.wikimedia.beta.wmflabs.org/wiki/File:Tatatatakk6_5.jpg
- add/edit/delete any statement
- click 'cancel' on the statement panel where you've made the change
- EXPECTED: a dialog box asking are you sure you want to discard your changes
- ACTUAL: no dialog box, changes discarded
Acceptance Criteria:
- as above, but with EXPECTED instead of ACTUAL