Attempt to graceful shutdown in case of panics (#8999)

* Handle graceful shutdown with unwinding

* Fix a race condition

* Avoid double exit deadlock

* typo: fix docs

* Fix ethkey cli compilation

* Fix all other cases panic_hook::set -> panic_hook::set_abort

* struct fields do not need to be public

* Add comments on why exiting AtomicBool is needed

whisper/cli/src/main.rs

@@ -184,7 +184,7 @@ impl fmt::Display for Error {
 }
 
 fn main() {
-	panic_hook::set();
+	panic_hook::set_abort();
 
 	match execute(env::args()) {
 		Ok(_) => {