[golemfactory/golem] SubtaskStatus is kept in two places (#3173)

@badb said:
> the state in task manager represents Golem knowledge about child task state. Core task object represents apps knowlege about child task state.
> Golem knowledge should come from app
> App, ie. task (so Golem Blender task)
> Golem should not care how apps classes are implented (apart from API (ie specific functions right now))

So, these two state machines should stay separate, with their own enums. Question is: what states should each have?