RFE: report warning when there is actor producing message that cannot be consumed

[pirat89]

I hit that already several times in different situations but I think this is good think that would be implemented. E.g. for CI or just for developers. Problem is that when actor is created, that produces or consumes some message, there can be situation that someone put the actor into a wrong phase so it would happen, that actor (A) consuming message (M1) is processed in phase before actor (B) producing message (M1). So the message is never consumed and sometimes it's not clear what is the problem - especially for people not so familiar with all actors.

Not sure whether the warning message should be printed by the framework itself or just by snactor (or completely separate script e.g.). What about to have something like:

 $ snactor repo check

I know this is not something that will save world, but something like that would help to do at least fast overview over the repository and it would show some obvious problems sometimes. Maybe we should think about more stuff we can do here. But basically, what do you thing about that? Anyway, it's just nice to have.