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/GClipboard.h

@@ -0,0 +1,14 @@
+#pragma once
+
+#include <AK/AKString.h>
+
+class GClipboard {
+public:
+    static GClipboard& the();
+
+    String data() const;
+    void set_data(const StringView&);
+
+private:
+    GClipboard();
+};