feat: user comment should provide also user display name and profile picture

**Is your feature request related to a problem? Please describe.**
When we display comments we want to see who made the comment and see profile picture.

**Describe the solution you'd like**
Add used node to comment which contains user display name and profile picture

**Describe alternatives you've considered**
not nesting those values under user but it is less elegant or attaching all user information which is overwhelming

**Additional context**
current json response looks as follows:
```
[
{
"id": 1,
"user_id": 2,
"task_id": 1,
"relation_id": 1,
"creation_date": 1581885745.451706,
"modification_date": null,
"comment": "test comment"
}
]
```