Turn LoggingAdapter to an interface and add new baseclass

Rename LoggingAdapter to LoggingAdapterBase.
Add new interface LoggingAdapter.
Make Logging.GetLogger an extension method on IActorContext

The preferred way of getting a logger inside an actor is:
private readonly LoggingAdapter _log = Context.GetLogger();
Remove LastWasNoMsg from TestKit

It's not supposed to be public
Merge pull request #467 from HCanber/remove-lastwasnomsg

Remove LastWasNoMsg from TestKit
Merge pull request #454 from HCanber/ilogger

Replace LogAdapter with ILogger
Test that proves #469 ReceiveTimeout isn't cancelled on termination
Cancel ReceiveTimeout when actor terminates
Timeouts should always be cancelled on CheckReceiveTimeout calls
Merge pull request #470 from HCanber/receivetimeout-cancelled-on-termination-469

ReceiveTimeout must be cancelled when actor terminates