Feature Request: Add an option in the UI for reverting background to random image, after setting a specific one

[thebolsh]

After setting a background (usually via the remote web interface), the only way to return to the previous behaviour which picks a background at random, we need to SSH/FTP in and rename files. This is a request to add the functionality to the UI.

[n-batalha]

As this is a monorepo, clarifying the scope: the above is wrt to the MiSTer Remote.

But it seems there are buttons to remove the set wallpaper (which makes it revert to random wallpapers), at least when the wallpaper is set via the app. Tested with the iOS app, to be confirmed on web.