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/GTextBox.h

@@ -0,0 +1,12 @@
+#pragma once
+
+#include <AK/Function.h>
+#include <LibGUI/GTextEditor.h>
+
+class GTextBox final : public GTextEditor {
+public:
+    explicit GTextBox(GWidget* parent);
+    virtual ~GTextBox() override;
+
+    virtual const char* class_name() const override { return "GTextBox"; }
+};