I would take a look at Larry Stout 's custom apps Larrys Custom WAB Widgets and More
If you check out his live preview and go to the Wha't's new page, you will see a user's preference reference
which might be what you are looking for.
I know Larry has changed jobs and is not necessarily working on this project anymore, and it may need some tweaks to work with the latest WAB, but he has quite a bit of information available on using his custom environment, so worth a look.
For this and other custom widgets, you may want to checkout my Web AppBuilder Developer Edition - Customization Resource List I typically keep it up to date, in not necessarily well formatted due to limited time.