quit/wait in Actor specialization

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[subscriber] handler as Qt object cares about unsubscription better

Signal can be already null and handler on deletion cares about signals
too

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
Merge pull request #7 from nemomobile/dont-disconnect-dead-signal

Don't disconnect dead signal