Add issueable actor

**What does this MR do?**
shows who performed an action on issue and merge request
**Are there points in the code the reviewer needs to double check?**
- https://github.com/Bugagazavr/gitlabhq/compare/issue-actor?expand=1#diff-f5d75b3f51cff6951def38500e8f1d5bR11
- https://github.com/Bugagazavr/gitlabhq/compare/issue-actor?expand=1#diff-ea522eaf75db2e90cd4aa98f86660ecdR16
- https://github.com/Bugagazavr/gitlabhq/compare/issue-actor?expand=1#diff-cfc01263b757d0733a45a5b20d548722R16

**Why was this MR needed?**
For many chats, to get many information who performed action

```json
{  
   "object_kind":"issue",
   "user":{  
      "name":"Administrator",
      "username":"root",
      "avatar_url":"http://www.gravatar.com/avatar/e64c7d89f26bd1972efa854d13d7dd61?s=40\u0026d=identicon"
   },
   "object_attributes":{  
      "id":77,
      "title":"Saepe odit vel et nihil illo qui corporis modi.",
      "assignee_id":20,
      "author_id":20,
      "project_id":8,
      "created_at":"2014-10-05 12:30:03 UTC",
      "updated_at":"2014-10-05 13:00:25 UTC",
      "position":0,
      "branch_name":null,
      "description":"A reiciendis et laborum.",
      "milestone_id":26,
      "state":"closed",
      "iid":7,
      "url":"http://localhost:3000/h5bp/html5-boilerplate/issues/7",
      "action":"close"
   }
}
```
Pedantic: Could you make the whitespace same as for the other elements?