[REST API] [SERVICE] Attachments

Create new way to add attachments to article

* [x] Attachment entity
* [x] Article Attachments entity (not neede - we used relation)
* [x] REST API - article attachments /api/articles/{id} - attachments are there if available 
* [x] REST API - article images /api/articles/{id}/{language}/images
* [x] Translation  entity
* [x] Attachment service
* [x] REST API - get
* [x] REST API - list
* [x] REST API - create
* [x] REST API - update
* [x] REST API - delete
* [x] REST API - attachments link
* [x] REST API - images link
* [x] rewrite to symfony controller broken attachment.php file
* [x] phpspec2 specs
* [x] behat api tests