Added a cli method to check the visibility of a window. (#301)

globals.d.ts

@@ -6,6 +6,7 @@ import { Options, Variable as VariableType } from 'types/variable';
 declare global {
     var globalMousePos: VariableType<number[]>;
     var useTheme: (filePath: string) => void;
+    var isWindowVisible: (windowName: string) => boolean;
     var globalWeatherVar: VariableType<Weather>;
     var options: Options;
     var removingNotifications: VariableType<boolean>;