Libraries: Create top level directory for libraries.

Things were getting a little crowded in the project root, so this patch
moves the Lib*/ directories into Libraries/.

Libraries/LibGUI/GMenuBar.h

@@ -0,0 +1,25 @@
+#pragma once
+
+#include <AK/Badge.h>
+#include <AK/Vector.h>
+#include <LibGUI/GMenu.h>
+
+class GApplication;
+
+class GMenuBar {
+public:
+    GMenuBar();
+    ~GMenuBar();
+
+    void add_menu(OwnPtr<GMenu>&&);
+
+    void notify_added_to_application(Badge<GApplication>);
+    void notify_removed_from_application(Badge<GApplication>);
+
+private:
+    int realize_menubar();
+    void unrealize_menubar();
+
+    int m_menubar_id { -1 };
+    Vector<OwnPtr<GMenu>> m_menus;
+};