Added clock unschedule to stop, clear=true method
started to reorganize world object and platform code, switching machines
foreground is no longer dependent on world object
removed stray code
edited object render
Fixed double entry of coins in world_objects list
removed some useless code I had put in
Merge branch '33-stop-particle-update-a' into master_candidate
Merge branch '34-separate-world-object-and-platform-code-a' into master_candidate