selection: Create it's dedicated class

includes/context.hpp

@@ -19,6 +19,8 @@ class Render;
 namespace gol {
 class SettingsMenu;
 class SelectionMenu;
+class ControlMenu;
+class Selection;
 
 typedef struct ctx {
   std::shared_ptr<World> world = nullptr;
@@ -26,6 +28,8 @@ typedef struct ctx {
   std::shared_ptr<Render> render = nullptr;
   std::shared_ptr<SettingsMenu> settings_menu = nullptr;
   std::shared_ptr<SelectionMenu> selection_menu = nullptr;
+  std::shared_ptr<ControlMenu> control_menu = nullptr;
+  std::shared_ptr<Selection> selection = nullptr;
   nlohmann::json config_json;
 } ctx;