LayoutConfig: Added option to define screen-wide background

src/types/LayoutConfig.ts

@@ -2,6 +2,7 @@ import {PanelTypes} from "../panels/_Panels";
 
 export type LayoutConfig = {
   id: string,
+  background?: string,
   schedule: LayoutSchedule,
   panels: PanelDefinition<any>[]
 }