Start working on a Widgets library.

Widgets/AbstractScreen.h

@@ -0,0 +1,25 @@
+#pragma once
+
+class Widget;
+
+class AbstractScreen {
+public:
+    virtual ~AbstractScreen();
+
+    unsigned width() const { return m_width; }
+    unsigned height() const { return m_height; }
+
+    void setRootWidget(Widget*);
+
+    static AbstractScreen& the();
+
+protected:
+    AbstractScreen(unsigned width, unsigned height);
+
+private:
+    unsigned m_width { 0 };
+    unsigned m_height { 0 };
+
+    Widget* m_rootWidget { nullptr };
+};
+