do not start break when there is another full screen window

It might be nice to not start a break when there is another full screen window open.

If you're watching a movie, then you don't want break-time to pop-up over the movie window.

There is some existing code to get the window title of every X window here:

https://github.com/cdepillabout/break-time/blob/6bad134cf96089ebd0ee372412d83d896b9f8633/src/scheduler/plugins/window_titles.rs

Maybe some of this code could be adapted to also checking if every X window is full screen or not. However, I'm not sure how this would work, or if it is even possible with X.