PhpDoc fixes for all the comment manager related classes

Greetings,

While working with PHPStorm I noticed some PhpDoc problems with the comment manager classes.  So I decided to clean them up.

- Removed all the conflicting phpdoc in the classes with ```{@inheritdoc}```.
- This also fixed some errors like https://github.com/FriendsOfSymfony/FOSCommentBundle/blob/master/Entity/CommentManager.php#L67 (returns comments, not threads)
- Improved IDE autocompletion by replacing things like ```@return array An array of CommentInterfaces``` with ```@return CommentInterface[] An array of CommentInterfaces```.