Add a reset button to the tutorial editors

[AbhayVAshokan]

Please add a reset button to the tutorial editors. A browser refresh does reset the current editor state. A dedicated button to reset the editor may add a better UX.

[AloisSeckar]

This would go to vuejs/repl where the editor component is being maintained

They added a toggle button recently, so this should be a good hint of how to do it vuejs/repl#283