Generator interfaces that plugins implement to add new generators.

### Create a new Generator

1. Create a new module, and set `GeneratorAPI` as a dependency.
2. Create a new class that implements `Generator`. Because `Generator` interface extends `LongTask`, add `LongTaskAPI` as another of your module dependency.
3. Add @ServiceProvider annotation to your class to declare you are implementing a Generator service. Put `Generator.class` as the annotation service parameter.
4. Implement `GeneratorUI` if your generator needs a settings panel and return it from `getUI()` method.