/graph api PATCH requests should by default not return a body

sth like
```
PATCH https://cloud.ocis.test/graph/v1.0/users/{id}
Content-type: application/json

{
"displayName": "Test User"
}
```

should return
```
HTTP/1.1 204 No Content
```

without a body.

If the representation is needed clients can send a `Prefer: return=representation` header.

See http://docs.oasis-open.org/odata/odata/v4.01/odata-v4.01-part1-protocol.html#_Toc31358878

Currenty, the /users endpoint always returns the full object.