Provide a generic entity revert controller.

Add a content entity form which allows to set revisions

Provide contextual links for all entity types

The trait and interface didn't matched

Rendered entity

Add a route provider and controller for add page/form.

- removed the classes to match core behavior.
- started using the link object.
- Added an interface for bundle entity descriptions.
- dawehner's fix for create_bundle_url in the preprocess function.

Add a revision view controller /node/{node}/revisions/{revision_id}