Add pagination info to get results whatever the HATEOAS status

This is breaking the backward compatibility of collection responses when
HATEOAS is disabled. Collection responses now get always the same response
format. HATEOAS status does only affect the presence or not of the _link
section.

New collection response format is as follow:

```json
{
    "_total": 1234,
    "_page": 1,
    "_max_results": 20,
    "_items": [
        ...
    ]
}
```

Fixes #355