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/GGroupBox.h

@@ -0,0 +1,20 @@
+#pragma once
+
+#include <LibGUI/GWidget.h>
+
+class GGroupBox : public GWidget {
+public:
+    GGroupBox(const StringView& title, GWidget* parent);
+    virtual ~GGroupBox() override;
+
+    String title() const { return m_title; }
+    void set_title(const StringView&);
+
+    virtual const char* class_name() const override { return "GGroupBox"; }
+
+protected:
+    virtual void paint_event(GPaintEvent&) override;
+
+private:
+    String m_title;
+};