Adding reload/restart dialog

# Adding reload/restart dialog
# Summary

Hi, I like your project and I've been using it recently. but I found a missing dialog in the **Preferences** part because when I hit **Enable fixed-width layout** I have to reload the page or if I have it installed on my chrome browser I have to restart the app to take effect, so I thought it would be good to add a dialog in front of the text as I did in the picture below, and also if it's possible I would like to contribute and send a pull request if I'm allowed.

Thank you :)

## Examples


**OR**


Start from the Preferences entry point and reproduce enabling “fixed-width layout” in both the browser and installed Chrome app. Compare the current behavior with the linked examples; done means a reload/restart dialog is shown for this setting and the behavior is checked in both contexts.

Scritto dal modello di indicizzazione a partire dal testo della issue.