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/GPainter.h

@@ -0,0 +1,12 @@
+#pragma once
+
+#include <SharedGraphics/Painter.h>
+
+class GWidget;
+class GraphicsBitmap;
+
+class GPainter : public Painter {
+public:
+    explicit GPainter(GWidget&);
+    explicit GPainter(GraphicsBitmap&);
+};