Implemented setter of wanted_metrics.

Also:
- Made unit tests.
- Refactored the method parse_supported_metrics to return an instance of NativeMetric instead of an instance of Metric
- Refactored the factory of metrics to create support the creation of an analizo_native_metric
- Refactored the factory of languages to support the creation of languages with :CPP and :JAVA types
Using the analizo_native_metric factory.