Warn the user if they are leaving a story edit page with unsaved changes

[arielj]

Branch/Commit:

Main branch

Describe the feature:

It would be nice to be warned that you have unsaved changes if you are going back/clicking a link/closing the tab, so a click somewhere by mistake does not clear whatever was being done.

Problem:

Currently, if you click in the wrong place or press the wrong key combination to leave the current page, you can lose information that was not saved.

I will abide by the code of conduct

[JuanVqz]

Open PR #334 implements this (warns before leaving the story edit page with unsaved changes). Leaving this issue open; it will close when that PR is merged.