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/GInputBox.h

@@ -0,0 +1,25 @@
+#pragma once
+
+#include <LibGUI/GDialog.h>
+
+class GButton;
+class GTextEditor;
+
+class GInputBox : public GDialog {
+public:
+    explicit GInputBox(const StringView& prompt, const StringView& title, CObject* parent = nullptr);
+    virtual ~GInputBox() override;
+
+    String text_value() const { return m_text_value; }
+
+    virtual const char* class_name() const override { return "GInputBox"; }
+
+private:
+    void build();
+    String m_prompt;
+    String m_text_value;
+
+    GButton* m_ok_button { nullptr };
+    GButton* m_cancel_button { nullptr };
+    GTextEditor* m_text_editor { nullptr };
+};