Mario: add basic main menu to editor, separate scenes from main game loop

mario/CMakeLists.txt

@@ -89,6 +89,8 @@ target_sources(editor
 	PRIVATE edit_box.cpp
 	PRIVATE tool_box.cpp
 	PRIVATE editor_visitor.cpp
+	PRIVATE scenes/editor_main.cpp
+	PRIVATE scenes/editor_main_menu.cpp
         )
 
 target_compile_definitions(editor PUBLIC EDITOR)