Tracking output state

[pgebal]

How precise do we want to be in tracking output state?
Currently output can be:

- "pending": the default state when creating an output
- "confirmed": the output is confirmed on the rootchain
- "exiting": the output is being exited
- "piggybacked": the output is a part of an IFE and has been piggybacked

If we want to be really precise why not mark output as challenged or exited?

I don't see benefits for tracking state in greater detail than, pending, confirmed or spent (general name for exited or used as an input for other transaction). What are those benefits?

[pgebal]

To sum up:

1. Marking as challenged or exited introduces additional complexity and is not necessary, we spent output when standard exit is started or ife is piggybacked. We'll still get this info from watcher, which has to track state more precisely than childchain.
2. When it comes to having outputs "exiting" and "piggybacked" I think that was a product requirement but I don't remember why/ @Pongch @mederic-p do you guys remember why?