ActorSystem lifetimes

[longshorej]

It'd be great to, where possible, have relevant lifetimes tied to that of the ActorSystem, rather than 'static as they are now.

[longshorej]

Streams make use of Any (to hide Ctl types from consumers), so a Flow's In/Out/Ctl types will need to remain 'static.

Relevant:
https://www.reddit.com/r/rust/comments/2r25rf/why_does_any_only_work_for_t_static/
https://doc.rust-lang.org/std/any/