[Core] Adds PreUpdateDocumentsSubscriber

Introduces PreUpdateDocumtsSubscriber:
* Allows Entities to change or set certain values prior to persistence.
* Tracks also NEW documents.
* Adds PreUpdateAwareInterface: Entities implementing this will be handled by
  PreUpdateDocumentsSubscriber.

* Adds title attribute to the barrating div generated by the rating view helper.

(references gh-15)
[Applications] Finished comments and rating system.

* Refactors javascript
* Adds create and edit actions to CommentController
* Enhances: Rating display on detail page will refresh after comment creation or editing.

(references gh-15)