Prototype for confirming return from break

[Wallby]

As comment on #396

What would suffice is that instead of automatically restarting the timer after 2 minutes, the transparent overlay with the notification in the middle (for the break) will display a button with the text "I'm back". Which you have to press to close the overlay. And restart the timer.

I am not experienced in these languages/tools. It is a working prototype. Probably could be implemented better. But demonstrates the concept.