Applets: Add DesktopPicker applet

This applet displays a grid of desktops, and shows the user what virtual
desktop they are on. When clicked, the desktop will be changed.

Userland/Applets/DesktopPicker/DesktopStatusWindow.h

@@ -0,0 +1,25 @@
+/*
+ * Copyright (c) 2021, Peter Elliott <pelliott@ualberta.ca>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibGUI/Window.h>
+
+class DesktopStatusWidget;
+
+class DesktopStatusWindow : public GUI::Window {
+    C_OBJECT(DesktopStatusWindow);
+
+public:
+    virtual ~DesktopStatusWindow() override;
+
+    virtual void wm_event(GUI::WMEvent&) override;
+
+private:
+    DesktopStatusWindow();
+
+    DesktopStatusWidget* m_widget;
+};