Interfaces for creating new statistics and metrics algorihms.

### Create a new Metrics

1. Create a new module and set `StatisticsAPI` and `GraphAPI` as dependencies.
2. Create a new builder class by implementing `StatisticsBuilder`
3. Add @ServiceProvider annotation to your builder, that it can be found by the system. Set `StatisticsBuilder` as the annotation parameter.
4. Create a new class that implements `Statistics`. Write you code in the `execute()` method.
5. Create a new class implementing `StatisticsUI` and add @ServiceProvider annotation as well.
6. In both `StatisticsBuilder` and `StatisticsUI`, return your `Statistics` class object for the `getStatisticsClass()` method.

To let your export task be cancelled and its progress watched, implement `LongTask` interface.