lomiri-system-settings: Cannot revert background image to system default

Lomiri in Debian (and other distros, as well) are pre-configured with a default background image (system default).

After having configured a customer background (either from the list of available Lomiri wallpapers or some own background image stored in $HOME) it is not possible to revert the setting back to system default.

This issue is considered resolved if there is a UI element available in the background image settings UI of lomiri-system-settings that the user can use to revert the background image back to system default.