Simplified implementation for Drupal 8

I spend some time on understanding Drupal 8 plugin system and api. I've come up with following implementation

1. Define AuthorPane plugin ( Service, Annotation and BaseClass)
2. There is no need to define custom entity, (BTW plugins are entity itself).
3. Theme function will be called from plugin itself not block, this will help others in who wants to display it other way, so they can create AuthorPane plugin their way, and they don't have to alter block. Template and theme will be in that module it self.