Change global widget container to page

include/gui/Page.hpp

@@ -0,0 +1,27 @@
+#pragma once
+
+#include <vector>
+#include <memory>
+
+namespace mgl {
+    class Event;
+    class Window;
+}
+
+namespace gsr {
+    class Widget;
+
+    class Page {
+    public:
+        Page() = default;
+        Page(const Page&) = delete;
+        Page& operator=(const Page&) = delete;
+
+        void add_widget(std::unique_ptr<Widget> widget);
+
+        void on_event(mgl::Event &event, mgl::Window &window);
+        void draw(mgl::Window &window);
+    private:
+        std::vector<std::unique_ptr<Widget>> widgets;
+    };
+}