handle ctrl+c and cleanup before exit

Since we need to cleanup actors and miner both with or without panic, I thought it'd be best to just use `defer` without `recover`. I tested this and found that panic or not, defer cleans up as expected. If I'm missing some case where `recover` is required, let me know.

Ctrl+C was being propagated to any spawned processes so strictly speaking the handler here is superfluous. Just thought it would be a good practice to not rely on the caller (`os/exec`?) and clean it up anyway.
If I understand it correctly, there are two things here: 1) Actor managing it's own goroutines and 2) Main managing multiple Actor goroutines. We'll need another waitgroup in Main (as we had earlier) which will have `actorsAmount` items each running an actor. Internally actor could have goroutines for doing stuff like sending addresses upstream and creating transactions in different goroutines.