Introduce callback for successful reconnection

These commits introduce an `onReconnected()` callback to `IBaseCastConsumer`. Seeing as most events have a proper callback in the CCL, I was sad to see this one was missing.

If you use `reconnectSessionIfPossible()`, there is no callback being called to notify you (as far as I've been able to find). I decided to implement this in CCL itself.

This callback has been requested before, in issue #99.
I don't know whether CCL is still in a code freeze, but would love to see this implemented.

Thanks,
Tolga Paksoy