Implement EventFilter in TestKit

Fixes #323.

Contains mainly additions except:

- `DefaultLogger` was refactored so that instead of logging directly to `Console` it calls the overridable `Print`. Also converted it to `ActorBase`
- Introduce `Warning()` in `LoggingAdapter`. 

## Discussion ##
`LoggingAdapter` already has Warn methods, but to be consistent with `Debug()` logging an instance of the `Debug` class, `Info()` an `Info` class, `Error()` an `Error` class, we should have a `Warning()` logging a `Warning` class, and make `Warn` obsolete. Thoughts?