Confirm discard changes
What does this MR do?
Prompt the user if they attempt to navigate away from editing file, before content has been saved.
Are there points in the code the reviewer needs to double check?
Not that I am aware
Why was this MR needed?
Users could accidentally discard their changes by clicking a link
What are the relevant issue numbers?
Screenshots (if relevant)
Chrome 50.0.2661.75 (64-bit)
![chrome] (/uploads/209ddbd7be1c775c14ac631519ad3f0c/chrome.jpg)
Firefox 45.0.2
