Force-reload background image on config reload

Make it possible to see the change without restarting Mirage if an
image used for the theme's background was edited, or if used did the
mistake of typing "/path/to/img" then corrects it to
"file:///path/to/img".

src/gui/UI.qml

@@ -32,7 +32,10 @@ Item {
     readonly property alias idleManager: idleManager
 
     function reloadSettings() {
-        py.loadSettings(() => { mainUI.pressAnimation.start() })
+        py.loadSettings(() => {
+            image.reload()
+            mainUI.pressAnimation.start()
+        })
     }