Comments API + attachments updates

                      
| Q             | A    |
| ------------- | ------------- |
| Bug Fix?:     | n    |
| New Feature?: | y    |
| BC Breaks?:   | n    |
| Deprecations?: | n    |
| Tests Pass?:  | y    |
| License:      | GPL-3 | 

Comments REST API
* [x] GET /comments # for all
* [x] GET /comments/{commentid} # single comment
* [x] GET /comments/article/{articleid}/{languageid}/ # for all
* [x] GET /comments/article/{articleid}/{languageid}/recommended # for recommended
* [x] POST /comments/article/{articleid}/{languageid}/ # insert new comment
* [x] PATCH /comments/{commentid}
* [x] PATCH /comments/article/{articleid}/{languageid}/{commentid}
* [x] DELETE /comments/{commentid}
* [x] DELETE /comments/article/{articleid}/{languageid}/{commentid}

Provide REST API for Comments resource + fix some attchments stuff