Start adding a Window class.

Widgets/Window.cpp

@@ -0,0 +1,39 @@
+#include "Window.h"
+#include "WindowManager.h"
+
+Window::Window(Object* parent)
+    : Object(parent)
+{
+    WindowManager::the().addWindow(*this);
+}
+
+Window::~Window()
+{
+}
+
+void Window::setMainWidget(Widget* widget)
+{
+    if (m_mainWidget == widget)
+        return;
+
+    m_mainWidget = widget;
+}
+
+void Window::setTitle(String&& title)
+{
+    if (m_title == title)
+        return;
+
+    m_title = std::move(title);
+    WindowManager::the().notifyTitleChanged(*this);
+}
+
+
+void Window::setRect(const Rect& rect)
+{
+    if (m_rect == rect)
+        return;
+    auto oldRect = m_rect;
+    m_rect = rect;
+    WindowManager::the().notifyRectChanged(*this, oldRect, m_rect);
+}