For each engine:
- Make a new folder detection
- Move detection-related files inside the folder
- Add a new module "enginename/detection"
- Add DETECT_OBJS here
- Adjust the normal engine module to remove detect_objs
- Adjust every file for the new changes.
- Move detection code used by createInstance & MetaEngine to a common header - detection_internal.h
- Move steam-related method & table to detection_steam.h
- More info in comments.