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/GModelEditingDelegate.h

@@ -0,0 +1,60 @@
+#pragma once
+
+#include <LibGUI/GModel.h>
+#include <LibGUI/GTextBox.h>
+#include <LibGUI/GWidget.h>
+
+class GModelEditingDelegate {
+public:
+    GModelEditingDelegate() {}
+    virtual ~GModelEditingDelegate() {}
+
+    void bind(GModel& model, const GModelIndex& index)
+    {
+        if (m_model.ptr() == &model && m_index == index)
+            return;
+        m_model = model;
+        m_index = index;
+        m_widget = create_widget()->make_weak_ptr();
+    }
+
+    GWidget* widget() { return m_widget; }
+    const GWidget* widget() const { return m_widget; }
+
+    Function<void()> on_commit;
+
+    virtual GVariant value() const = 0;
+    virtual void set_value(const GVariant&) = 0;
+
+    virtual void will_begin_editing() { }
+
+protected:
+    virtual GWidget* create_widget() = 0;
+    void commit()
+    {
+        if (on_commit)
+            on_commit();
+    }
+
+private:
+    RefPtr<GModel> m_model;
+    GModelIndex m_index;
+    WeakPtr<GWidget> m_widget;
+};
+
+class GStringModelEditingDelegate : public GModelEditingDelegate {
+public:
+    GStringModelEditingDelegate() {}
+    virtual ~GStringModelEditingDelegate() override {}
+
+    virtual GWidget* create_widget() override
+    {
+        auto* textbox = new GTextBox(nullptr);
+        textbox->on_return_pressed = [this] {
+            commit();
+        };
+        return textbox;
+    }
+    virtual GVariant value() const override { return static_cast<const GTextBox*>(widget())->text(); }
+    virtual void set_value(const GVariant& value) override { static_cast<GTextBox*>(widget())->set_text(value.to_string()); }
+};